No, there is practically nothing you can do to get 4 confirmations faster than 40 minutes on average.
You need to check your assumptions. Why do you need 4 confirms? Double-spending is very unlikely to be a problem for physical PoS. In the future there will be ways to get instant confirmation for payments.
You're right. Like I said in a previous reply, I was trying to overprotect my merchants. No need to do that since most merchants aren't going to be doing $5m sales in Bitcoin. Double spending really wouldn't be worth the effort for small transactions and, by the time Bitcoin is being widely used for large ones, there will be better systems in place for confirmations.
Thanks!