How to add NMI recurring payment?

I want to add recurring payment in NMI using ruby on rails.

I added simple payment.

gw.doSale("5.00","4111111111111111","1212",'999')

See example : http://ift.tt/1wHaxn3

But I need recurring payment so I can get subscription_id in the response and I will store in database.

I have some example for recurring but not getting how to add

See Example: http://ift.tt/1wHaxn5

Please help me, How to add recurring payment