Ok, i think its time to contribute this:
You know, since Pets dissapear if you mount they get lesser Hp and mana if they are below 100%.
But this works also in the different way:
1. First you need "Dark Pact"
2. If you want your Pet full mana, tap it to zero.
3. show at the Manabar from your pet and exactly (0-1 sec) after it got a manatick use "Dark Pact" and at the same moment Mount up (Mount dont has the normal global cooldown so you can do this 0.1 sec after DP)
4. If you have done it right, you mount up with 0 Petmana (thats important)
5. Wait some seconds (mostly also works if you only mount up 1 sec) and dismount and your pet has 100% Mana
Shortversion: If you mount up, when your pet has exact 0 Mana, it has 100% after dismount.
I Use this since a long time (Exactly since blizzard nerved it that pets always has 100% Mana and HP after Mountup).
Maybe also work for non DP Warlocks if you time a Petspell right...
/Edit: VIDEO -> Watch it, live Realm europe Patch 2.3.3
Pet_Mana_Exploit.avi - FileFront.com