I would soak them in a 50/50 mix of white glue and water and then place them where you want them. It wont seem like it is working or sticking at all, but leave them alone until it is all the way dry and they will be very securely attached. It can take half a day or even longer but it works well and you wont see any trace of the glue when its dry.
Just did some yesterday using that technique.....works great.