http://www.caa.co.uk/docs/49/Process...0of%20SOLI.pdf
SRG1202: Form for the Transfer of Medical Details to the UK CAA Medical Section for a Change of State Licence (SOLI) | Publications | About the CAA
Once the medical stuff is transferred then it isn't to bad.
I don't know anyone recently that has done it.
You will have to get some sort of EASA medical valid to be able to get the license issued. But there are doctors in the US that can do it.
AME Search Results | Medical | Personal Licences and Training
Much as people bitch about the UK fee's its not going to cost that much to do.