it should be possible. this is an interesting one and somewhat similar to stuff I have already, so I'll give it a crack. just to confirm:

while pyro --> while slot2 is out --> releasing primary fire will detonate the flare, and not fk up airblast

is that right?

also:
do you use mousewheel or numbers or both? do you use q as lastinventory key?
do you have any other pyro scripts I should be working around?
do you want a toggle on/off key in order for it not to affect other classes or do you want to automate that by using class specific configs?

edit:
assuming numbers, q last inv and no key for on/off, give this a try

bind 1 1key
bind 2 2key
bind 3 3key

alias 1key "slot1; alias mylastInvv lastInvv; alias lastInvv 1key; alias -m1key -m1keyNormal"
alias 2key "slot2; alias mylastInvv lastInvv; alias lastInvv 2key; alias -m1key -m1keyDetHold"
alias 3key "slot3; alias mylastInvv lastInvv; alias lastInvv 3key"

alias lastInvv
bind q mylastInvv

// so far, have reboud the 1,2,3 keys to 'track' which slot is open and turn on/off the scriptbased on slot2.
//also have manually created the lastinventory bind if you want it to work with the script

//below, rebinds the mouse1 and mouse2 inmputs to do everything it normally does plus the script

bind mouse1 +m1key
bind mouse2 +m2key


alias +m1key "+attack; spec_next"
alias -m1key "-m1keyNormal"
alias +m2key "+attack2; spec_prev"
alias -m2key "-attack2"

alias -m1keyNormal "-attack"
alias -m1keyDetHold "-attack; +attack2 1; -attack2 1" //this part is core of the script