A subscription that moves from Finite period to a Serial one

I have a new buddypress Membership site that needs to bring a large set of existing members over from an old site.

They were all signed up in Nov 2014 so the best thing is to give them an 8 month finite membership and then have them move to the normal 1 year serial membership. We are using the Standard Paypal gateway.

Can I set a subscription plan to start at 8 months Finite and move to 1 year serial? When I try to do this it pops up saying that it's using 2Checkout which is not what I want. Can you help please?