help with macro modifiers

[hlx]

hi there,
I never really got to understanding how mod/nomod work so I'm not sure if this is even doable.

right now I have a macro that simply casts two spells

/cast spell1
/cast spell2

what I would like to do is to modify it so that when I press lets say shift only "spell2" will be cast

/cast <holding shift blocks this> spell1
/cast spell2

is it possible? (and did I explained it correctly? )

[stevietv]

/cast [nomod:shift] spell 1
/cast spell 2

if not pressing anything casts spell 1 and spell 2
if pressing shift casts only spell 2


note that both these spells cannot trigger a global cooldown, otherwise only spell 1 will trigger.