I actually have got no problem with that because its more realistic, i dont think he will ever leave Barca (at least not in the near future) no matter the bid.
I don't agree with this. That level of realism should be reserved for league mode. Master league is not meant to be real. They let you play with anyone you want - I play as Cala Blanca - a personal favourite holiday resort in Menorca, they are sponsored by guitar manufacturer 'C.F.Martin & Co', not very realistic.
To help with the original question, buy Super Agent from the extra content menu, you will have to start a new ML and you will have to wait until you are in the top 10 club ranking or so, before you can sign the hyper stars. Aside from that, wait until he is old, going down and will probably end up on the transfer list.
I have the super agent and unlimited funds. The way I see it, I have done my realistic one and it got boring and annoying fast. Now I am actually having a bit of fun with ML. Be careful what you wish for though, I have had a lot of hyper players not do well and be very frustrating. This has been one of the 1st PES' that I can actualy use Messi. I have released Rooney and Ronaldo on this one because they didn't do too good for me, I got more out of Benzema(CF) and Taarabt(LWF), and they both started to go down.