Another way of doing it was described in another post on this forum. It's limited and has some requirements, but does work. You can use high level hunter or warlock pet(s) to help a group of lowbies get FULL XP for a kill.

First you put 2 or more lowbies in a group. This won't work with just 1 lowbie, you must have at least 2 grouped together.

You then need 1 or more high level hunters and/or warlocks following the lowbies around but NOT grouped with the lowbies.

Tag a mob with a lowbie and kill it with just the pet(s), DON'T use the hunter or warlock for any damage.

You will get full XP, though it will be split among the group of lowbies as usual. But that's a lot better than the crap XP you get when you have lowbies and highbies grouped together.

Becomes less effective as your lowbies level up and the mobs become harder or longer to kill with the pets.