DM-Deck16][?Game=PoopyMatchPlus?Mutators=InstantDeath
You can use next trick:
DM-Deck16][?Game=PoopyMatchPlus?Mutators=InstantDeath?-INI=UT.ini,?-USERINI=MyUser.ini,
?-
before term and ,
(comma) - after.This enough for pass parameters to engine.
In fact, last comma not necessary, since there usually come space, which too fit for end string as delimiter.