Nope, sorry. You can pay it off all at once and/or when you upgrade your phone, but that's it. I don't really know why you'd want to since they're pretty much paying it for you (aside from any Tab M or L contributions) so any extra that you contribute would just be burning more of your money.
Good news, though: there is a different way to make it go down faster: referrals! Start referring friends and family to Koodo and both you and the person signing up can receive $25 in Tab credits.