The only way i know is...
In QuestDiary/MapQuest_Def do a script like this. Linked to the mob you want killed to give extra grp exp
btw #if's dont work with this. it gives exp anyway i think.
#if
checgroupcount 2
#act
goto @1
[@1]
#act
GIVEEXP 500
------
That will give 500 exp for every grp member u have. If u got 6 ull all get 3k extra.
It shows up in the bottom corner as 500 6 times though if u got 6 members
You Received "Mobs base EXP"
You Receive 500 EXP
You Receive 500 EXP
You Receive 500 EXP
You Receive 500 EXP
You Receive 500 EXP
You Receive 500 EXP