One trick I use, although it might be risky with a brittle lozenge decal, is to coat the surface with Future just before laying down the decal. You have to work quickly and be very careful with placement since the Future starts to dry immediately. The decal can be moved before the future dries if necessary by slipping some water under a corner and working it around. As the decal dries, brush the bubbles to the edges. The Future will flatten out as it dries and that decal isn't going anywhere. Coat the decal surface with Future to seal it.
This has worked really well for me, but as I said, it might be risky with a large, brittle decal.
Joe