Currently, you have to do it with scripting. There are some examples in the wiki. For instance, something like below. Although the new undefined variables thing may not like it, and it could probably be cleaned up, but you get the idea:
[Script-rezgroup]
Commands=8
C1=/if ({RezChkTimer}) /return
C2=/if (!{Defined[RezChkTimer]}) /declare RezChkTimer timer outer 80
C3=/if (!{SpawnCount[corpse radius 50 group]}) /return
C4=/target id {Spawn[corpse group].ID}
C5=/delay 2s {Target.Type.Equal[corpse]}
C6=/corpse
C7=/call CastCall {Me.CleanName} ''cast rez {Spawn[corpse group].ID}''
C8=/varset RezChkTimer 80