I use granular T-7 in my .54 GPR and it works fine. If you still want to fire off the T-7 pellets in your rifle, you could load 5-10grs of granular T-7 and then load the pellets. The granular should be enough to contact the pellets igniting them reliably.
Of course this method is suited to range sessions only and should not be used in hunting situations.
Sidelocks rely on having a portion of the main charge spill over into the drum for ignition of the charge. Pellets sit too far away from the cap for the fire to reach it.
I also would suggest using #11M caps for T-7 and getting a Hot Shot nipple. I haven't had any ignition problems w/ #11s or T-7, but it dosen't hurt to Murphy proof your set up.