The Morley Dual Bass Wah (NOT Double Bass Wah... such a thing doesn't exist

) is spring-loaded.
The heavy-duty spring can be removed. All you need is a screwdriver and some patience. It's fairly simple in design. Be warned, however... if you want to put it back, it's going to be a pain.
I once disassembled an older Morley bass wah (the old blue one), and it wasn't fun getting the spring back in place.
On a related note... do you know what kind of wah sound you're looking for? Morley is very non-traditional (i.e., not like a Crybaby at all). But if it's the Morley sound you seek, and you don't mind a broad frequency sweep that cuts low end on some settings, why not consider their Power Wah reissue, which IS switched and not spring-loaded?