Is it possible to enclose payment with a business reply postcard, and still not pay postage?

I want to subscribe to a magazine through a business reply postcard, which says no postage necessary. But I'd like to enclose payment with the postcard, instead of just sending back the postcard by itself with the "bill me later" box marked. Can I send the postcard in an envelope together with a check? Then would I have to pay postage? How do businesses usually expect customers to do this?