If you have a scrap bezel with a good pip then pop it out, glue it into the good insert, and relume it. The method described on the other thread involving making a lens in place with epoxy is your best bet otherwise. If it isn't a vintage/collectable piece and original appearance isn't an issue, I usually mix my lume with the epoxy until the mixture is rather thick, then I fill the pip from the back, no lens.
If you're easy on the looks, but would like to have a plastic lens covering the lume, you might consider doing this.
Remove the bezel, lume the pip from behind (the surface tension from the lume binder would allow you to do that) and when it's dry, get a watch strap hole puncher (smallest punch) and punch a piece of plastic from say a CD cover, and stick it onto the hole where the plastic window should be using a little clear superglue. You may have to file the bezel opening a little or sand the plastic pip you've just made a little to have it fit properly so do it before you apply the lume.
This was brought up by a fellow Forum member whom I can't remember who it was sometime back and I've used this method with success. Was too lazy to source for a lume pip or dismantle another watch for this.
If you source a Pip Lens remember this: The lens is tapered to fit the insert from behind and can not be pushed through the front of the insert, No Glue needed as the binding agent in the lume holds the lens perfectly