I agree with the above. I didn't post initially because I thought my information might be dated. I believe submarine continuation pay, as well as having sufficient time to go back to a submarine, is also based on gates (i.e., having a cetain ratio of sub duty served versus time in service).
I have never heard of lump sum payments for submarine pay!
Disclaimer: From reading these boards, there are many things I don't remember or didn't think likely, so I'm just agreeing that the above post has been my experience.