In the end (there were 3 of us) we hired 3 bike boxes and had them couriered to Perpignan. They were there when we arrived no problem, we then packed our bike in to them and flew them back on Ryanair, no problems. Back at home the company sent a courier to pick up the boxes a few days later. Cost about £95 each including hire and courier costs. Suited us to do it, the hotel was accommodating to accept the delivery and store the boxes. All good, worth the money to take away to stress of using a bag or something like that.
The boxes were proper solid mounded plastic, good high end quality so there was never any doubt they would be shipped in safe order. There are quite a few companies out there that do this sort of service.
Cheers