Legally Marrying an Overseas Student whose Visa has expired

Dear Sirs,

I have been informed that this site provides unbiased advice to those requiring clarity on immigration laws. A friend of mine has been in the UK for approx. 4 years. He came in 2010 on a Tier 4 visa and was studying during this time. After two years he renewed his application but it was refused as the UKBA could not receive the funds for his renewal application. Rather than appealing on his initial Tier 4 application, he was advised to seek FLRO. This route however was refused. He now wishes to marry a UK Citizen but the UKBA has his passport.

Could you please advise what the best routes would be for him to legally marry this lady?

Thanks, in anticipation.

Rania.