best bet that works for me is to just go to your local kwik fit and give the boys cash in hand to fit them,usually charge about £30,dont go into the reception though just walk into the workshop and they might tell you to come back later
hope it works
My advice would be to avoid anywhere like kwik fit. What you want is a wee local place. The kind of place that looks dodgy as hell and has a guy about 80 doing the work.
Kwik fit are robbing barstewards. Smaller local places are usually happy to do that kind of work, and almost all tyre places will have facilities to do centreless rims