Use sprue tree with same color as the parts you want to glue / fill. Cut the sprue tree branch into small pieces, keep them in a small bottle such as used / cleaned paint bottle. Add some Plastic Magic just enough to cover the pieces of plastic and wait for couple of hours.
You can see the solution in the following picture. It feels much more sticky then the original Plastic Magic.
The melt material will fill the gap, wait for 24 hours and clean it with pen knife and sand it down with sandpaper.
This will mostly clean the seams, and you can barely noticed it. Depends on the sanding result, you might want to apply a matte clear coat to unify the color on sanded and non-sanded surface of the parts, and it should be good enough.
This technique can be used on parts which require gap filling but without painting afterwards.