First off let me give credit to Lenopi and Amalus (And I suppose Athene as well since he did this on wow years ago lol) for finding this first. I am making this post though as a guide to help continue you on your PL journey after level 22-29 in mandalorian raiders.
This is how I did this. Some of the things I say may not be necessary but it works. The flashpoint you use is "Boarding Party"
First off I made sure the level 44(or 50 or w/e you are using) is the "owner" of the flashpoint. To do this just go in solo and then invite the lower level.
Then fight your way to the "bonus" boss, the engineer with the 2 droid adds.
Once you make it there stand your low level in the square on the floor (the small one) that is just before the stairs leading down and then back up to the boss (the very tiny set of stairs right in front of the boss)
I used a level 44 marauder with Malavai Quinn as the companion. I turned off all of his dps abilities and left him on healing duty, although I am not sure that I would have even needed heals, I used him anyway. I DID NOT use a companion on the lower level (I do not know if that will change anything but since I was already playing 2 characters on 2 computers and controlling a companion on the 44, I didn't want to add anything else to my plate)
Now you are ready to pull, charge in on the main boss and give him a smack to make sure he is attacking you, and then start on his droids. The droids have about 41k hp and you need to keep them very close to the same HP the ENTIRE TIME. In order to do this I simply spammed my weak rage building "auto" attack on them back and forth. The real trick here is to keep the droids standing on the republic symbol on the floor. They can be standing anywhere on it, as long as they are touching it they are fine. The reason you do this is because when the boss causes the generators to explode it will always hit them both if they are touching that symbol, and do around 3700 dmg to them both.
The object here is to get both droids to 8k hp(or as close as you possibly can, below 7800 is bad and above 8300 can make it harder for the low level to kill them) at the same time and then have 2 generators hit them without you hitting them anymore. This will leave them at under 1k hp.
This is the really important part. Once they are around 1k hp you need to wait until the boss ignites a generator and VERY quickly run near the OPPOSITE side generator (if front left is lit up you run to back right) and as soon as you get to the other one (the idea here is to make sure the droids do not get hit by the ignited generator and die early) you click "exit area"
This can be very close. If you do it right, then the ignited generator will explode and not hit the adds, and then the boss will ignore a new one, and it will explode very shortly AFTER you exit the instance. More often than not the lat generator will explode and kill both adds right after you leave rewarding the low level the full amount of xp (18k total xp each run at 30 I believe)
If the generator does not kill the droids then the low level will need to pop any cooldowns necessary and kill the droids manually. (if you see that you will need to kill them manually you can start to dps them while the high level is still exiting area and get them primed for a quick kill)
As soon as the droids die you can run back towards the entrance of the room (right behind where I originally said the low level should stand) and reset the boss and respawn both adds.
After you get that down its easy, you just walk back in on the high level, mount up, and charge back down to the boss and start all over.
While learning this, doing it myself with 2 computers and 2 accounts, and using a level 44 instead of a 50, and including the time spent clearing my way to the boss, I spent around 4 hours for lvl 29-34 and averaged around 230k xp.
NOTE: its worth doing the same basic strategy on th champions leading up to the bonus boss just for a bit extra xp
Oh and just so you know if you are doing it quickly, you should be doing complete runs in 3-5 minutes, dont worry if you screw it up every now and then, I did plenty and still leveled plenty fast.