Joe -- In trying to envision what you're describing, I'm reminded of one unit I worked on where the lamps couldn't be snapped in either because the plastic was broken out -- almost as if an attempt was made to install too fat of a bulb. As with you, any attempt to install the correct bulbs simply had them fall out as a result of the broken plastic. I don't know if this is the case in your scenario, but my case, I was able to resolve the issue quite effectively by simply removing the one piece clip/electrical terminal at each end of each bulb, and reinserting them "backwards" (by 180 degrees). In this manner, instead of the bulb no longer snapping between the terminals which were originally oriented towards the outside of the receiver (with respect to the lamp), and the broken out plastic wall that was towards the inside, the bulb now snaps between the in tact plastic wall that is towards the outside of the receiver, and the terminal, which is now oriented towards the inside. With this repair, original style replacement bulbs simply snapped into place once again and were held firmly in place.
I hope this helps!
Dave