Trying to use PayPal Subscribe Button in a form

Hello,  I need to collect a series of information from a formscentral form which has PayPal payments integration enabled.  My problem is I find no option to intgrate PayPal using a subscription option for payment.  My only solution so far has been to collect information in the form and redirect after the submission to another web page which has the subscriber payment options.  The trouble with this is that the redirect happens in an iframe, and it's a little less than perfect looking as a result.

I'm using the subscribe button to offe ra free trial period and also offer annual and monthly subscription cost / payment options.

Can anyone help?

Cheers!