If you're only using the stick mapping in AH, here's what you need to do...
Under Stick Map 1, select stick map 2 with your pinkie.
Under Stick Map 2, select stick map 1 with your pinkie.
It won't do it only while it's held down, but while in stick map 1, if you depress the pinkie once it will select map 2, while in stick map 2 if you depress it once it will select map 1.
Making it a "depression" switch requires the use of the stick software from Saitek.