Reply to FX button, and releasing it properly with a shift button

Hey guys,
I'm currently mapping my MIDI fighter to my own likings (in Traktor Pro 2). But I'm having trouble releasing an FX button properly.

Suppose I have 2 buttons: A and B. B is set to trigger hotcue's, unless A is pressed. A is a 'shift' knob, which makes B trigger FX stuff. When A is pressed, B will set all sorts of FX settings ok (routing, dry/wet, select the FX and so on), and finally trigger an FX slot to be 'on'. The command is offcourse in 'hold' mode, because I want to release the FX when I release button B.

So far so good. BUT: when I accidently release A first, then B will stick: the modifier is reset to 0, and the 'FX On' command never recieves it's 'note off' command. So a workaround is needed to release the given (or all?) FX when I release A or B.

I have been trying out a few things, but either the FX would be triggered by A, or I would be triggering a hotcue... Also, sadly, in 'direct mode', the invert option in a MIDI command is unavailable...

Oh and I have a small limitation: M1 serves as my shift modifier, and M8 serves to select a deck. So within this FX On command I can't specify any more modifiers

So, does anyone have a suggestion that could help me making this mapping fool-proof, ie: releasing the given FX (or rather MIDI command in hold mode) wether A or B is released first?

Kind regards,
Johan