Need operator NOT in custom filters

Use case: I would like a custom filter for "Platform=NES" and NOT "Publisher=Romhacking".

This way, I can have two filters; one for NES Hacks and one for NES Roms which aren't hacks. I can think of a workaround but it involves manual entries in search fields and would require a lot of extra work to maintain (and may break if that field is needed for something else).