Howdy Alan,
Ok, I often use this particular product for creating "glass" on guages when i bother to do a model with alot of detail. And i think every modeller should have some of this product.....what is it you ask? Clear fingernail polish.
It wont fog clear parts and when creating the "glass" on guages, you simply apply a drop and allow to dry, it gives a nice glossy clear finish.
But, one of the other properties is has is that when its drying, it becomes "tacky". I believe it would be "tacky" enough to hold your lens in place until the polish dries.
I would simply apply it inside the tube, all around, give it a few minutes to become tacky, then insert the lens and allow it to sit until dry.
Not only is it good for guages, but for creating the illusion of lens covered navigation lights it works well too, simply paint whatever color you want the "light" to be on the model, then apply a few coats of the polish, allowing each coat to dry before the next coat.
Now this doesnt mean go steal your wifes clear figernail polish, really blow her mind and tell her that you need her to pick you up some lol.
Anyway, at about a dollar a bottle, get some and test it out for yourself, if you dont like it, it can be used in other applications like lens covers for guages and nav lights like i said.
Have a good day,
Greg