England Return Visa

I have a couple of questions about the VISA process for American citizens returning to the UK.

A little background: As mentioned, I am an American citizen. I am a recent graduate of a university and last year, I began working for a program that leads university students on a study abroad program. I went with the students and led them. I was paid by the American University and was required to have a Tier 5 Government Exchange Visa. My time of stay was from August-Decemeber of last year.

I have been asked to do the same program this year and have been assigned to go back to London. My simple question is: what Visa options are open to me?

I think I remember reading somewhere that the UKBA only sponsors the Tier 5 Visa once per person. Is that still the case? Is there a way I can extend the VISA that I already have? Is there another VISA that would work for me? I have been researching the Business Academic Visa. Would that work?

I do not leave until August, but I just wanted to get a jump on things in case I need to acquire certain documents or have different requirements. Any information would be more than helpful.

Thank you,

UPDATE ON THIS: I have heard that the VISA is not the main thing but the CAS number. If I have a new CAS number, then getting the Tier 5 VISA again is possible. The company I'm working for has already agreed to give me a new CAS number, so getting the Tier 5 again should not be an issue. Can anyone else confirm this?

I think you need a Certificate of Sponsorship (CoS).

A CAS is a Certificate of Acceptance for Studies, so that's not the right thing.

It looks like you can have this government exchange visa twice. The visa that's restricted to once in a lifetime is the youth mobility one.