I had the same problem of OK button doing nothing, only with hard pressing. I opened the remote starting at the round bottom. It took me 15 minutes with several creditcards, but finally I used the corner of the card on the points where the holes in the silver plastic is shown on the photo of josete2k.
That crunched some of the plastic inside but not on the exterior. Than I slided two cards on the length side of the remote. Opening the battery cap en putting a screwdriver into the hole at the button helped to wringe it open. Than the rest was peanuts.
The solution with aluminiumfoil worked for mee too.