I should have it released today. Please be aware of the below limitations.
1) Recurring only supports: Weekly, Monthly, and Yearly durations; other durations will attempt to convert.. invalid periods will throw an error during conversion and will be forced to single payment (this is always the fail safe)
2) Recurring is established after successful payment. If recurring fails it'll be forced to a single payment as payment was already successful.
3) Recurring requires an upgraded account, basic Advanced package does NOT include it.. if api call fails it'll force the purchase as a single payment
4) When express checkout is displayed it does not support recurring billing.. all purchases through it will be forced as single payment.. this is an issue on PayPals end failing to establish billing agreements when parameters are sent as recurring... express checkout can be disabled however
5) Bill me later was not tested, assumed works same as express checkout; test with caution
Note these limitations are due to PayPal and completely out of my hands. I'll provide the above as well as instructions once I've released it.