Question:
I have new L O T U S letters for my trunk. They include little plastic 'mouse condoms' that should fit into the drilled trunk hole, and the letter pegs fit into these and hold securely.

Well, the pegs do not fit. the drilled holes are roughly 3/16", and the pegs are maybe 1/8+ in. also, the pegs have a lip of about 1/16" to keep it from going too far... which will hold the letters up off
the boot even if I could fit them in the existing holes.

Answers:
The problem here is that the original tiny steel clips that slipped over the studs on the back of the letters & emblems are no longer available. These tensioned the studs in the holes and fit flush so there was no gap between the letters and bodywork.

You can goop a little silicone sealant on the back and stick the letters back on the trunk. I tried the factory approach and it works if all the holes are exactly the right diameter, 1/8" (freshly drilled), or if you fill the holes with touch-up paint you may be able to get them to stick. But why take a chance. I say just glue them on.

The back side of the boot lid outer skin is pretty well inaccessible on the Elan S3-S4, but you might be able to dab a bit of silicone onto the studs with drops on a screwdriver offered through the access holes on the inside.

A less satisfactory option would be to obtain double-sided emblem affixing tape from an auto body supply shop and stick the letters down directly to the paint.