dont bother!
for a start most bolt on necks joins have a little looseness, thats not really acceptable for a set-neck though
think about your gluing surfaces - they are probably both covered in paint which needs to be completely removed first and needs surfaces need to be smooth. by the point you are at that stage you will definately have a loose join unsuitable for a set-neck
there is the hack way to approach it which is to chuck a load of epoxy in the cavity and let that take care of it for you, but then you join is wood/paint/epoxy/paint/wood, and thats asking for trouble. even if it manages to be stable thing about what all that does for the tone
now if you have an unfinished neck designed to be a bolt on there is no real reason you cant glue it in if everything else is designed to allow for that
