am not certain whitch part you have glued..
If its the trigger adjustment nut, heres what to do
well, to be honest, Another Allen key might be worth trying..
(unless its the trigger grub nut thats rounded...)
But if its not, here is what i suggest, taking the trigger off your Ion with the Grub nut still firmly glued in place
Soak the trigger in hot water for a few hours, (obviously you will need to change the water) and then, with a fresh unrounded allen key, try to remove the nut..
Failing that, you could try and drill it out, but thats awkward without a bench drill, and would probably knacker the trigger..