I think centering does this just fine. You can´t use centering to lower the base TN, just to lower penalties. Because it´s much better to lower a penalty than to get an extra die, the best way of using centering is to sustain a spell, than toss spells using centering. If your not wounded allready. (Doesn´t help you do other stuff though. Hmm)

I don´t see anything wrong with such a metamagic. The issue just hasn´t come up in my group.