SOmetimes my client (whose site this is) gives 100% off

Hello! SOmetimes my client (whose site this is) gives 100% off coupon codes to people. Problem is, when they apply the coupon, it doesn't take them to paypal (because duh, they don't owe anything) so that extra added little step of them actually getting added to a subscription level, which usually happens after they pay, never happens, and they complain to my client, who then has to go and manually add them to a level. Is there any way possible to automate this so that if their coupon is for 100% off, they will go ahead and be added to the subscription even if they don't go to Paypal?