Wouldn't actually help much. Proc activation looks at the base recharge time, enhanced recharge time, area factor, activation time and... I forget what else. Enhanced recharge time does reduce proc chances, but not as much as the other aspects of the power.
A quick look at the sentinel T1 attacks shows that most have an unmodified proc rate of 29% with a standard 3.5 PPM proc. The 4s base recharge time, coupled with the 1.188s activation time, is why. Slotting a single level 50 RchgRdx IO only drops them to 22%, so spending a slot on a "negative Recharge" enhancement (which couldn't simply be a tweaked Slow enhancement, because being Slowed doesn't actually affect proc rates in any way) would, at best, only bring you back up to that same 29%.
Spending that same slot on another proc, however, gives you another 22% proc chance (assuming the same 42.4% slotted RchgRdx), which is muuuuuuuuuuuuuuuuuch better than anything you could regain from the "negative Recharge" enhancement. Really, in any power where you could slot the proposed enhancement, you'd be better served just using another proc. This "negative Recharge" enhancement would just be a newb trap.