I'd say you have a proper battle on your hands there fitting a DM4 CP roller trigger into an Impulse I frame.
Infact I'd say you'll have no luck what so ever, due to loads of reasons. Making the cp roller fatter to not jangle about in the gap for the I-Trigger would be one for a start.
The Impulse CP Roller can be fitted to a Smart Parts grip frame, no other, and it involves taking the stock one out and simply replacing it with the CP.
I'd sell your I-Frame if you like the roller, pick up a SP trigger frame and replace the bait SP trigger with the roller.