BD answered in
#dev. Pasting here for future peoples who may look at this thread.
%DIE1 := 1D4
%DIE2 := 1D4
%DIE3 := 1D4
%DIE4 := 1D4
%MIN := %DIE1
IF %MIN > %DIE2 THEN %MIN := %DIE2
IF %MIN > %DIE3 THEN %MIN := %DIE3
IF %MIN > %DIE4 THEN %MIN := %DIE4
%ROLL := %DIE1 + %DIE2 + %DIE3 + %DIE4 - %MIN