Well as you know, the difference between 280% and 60% is very big so here is a common sense tip:
for bombing run quest:
Run around on your land mount, being as evasive as possible
Find a group of 1-2 fel cannon balls you want to destroy
dismount
remount on your 225 flying mount
while casting the mount, right click the bomb
when you have mounted, quickly launch the bombs and dismount
You could make the dismounting easier by making a macro
also maybe /use Skyguard Bombs may work