I don't want to
diss anyone's suggestions, but, i have tried alot of these ideas and they haven't worked! (for me anyway .... calm down

)
Bicycle patch glue ; thumbs down, would not stick to the bladder (but different brands of glue may give different results on different bladders)
pool patch glue ; no good
tarzan grip (aqua) : no
araldyte : not a chance, peeled strainght off the bladder
the problem with most of these is they would not bond with the bladder material.
do a test on some scrap pieces before you try anything.
I have found the glue needs to be (and this is the important part) an ethylene or polyethylene based glue.
I bought a tube of ethylene glue from bunnings to do some valve repairs and it worked well (as long as i got the seal right)
I'll try to dig up the pot of glue when i get home and post it's name here.
but IMO the best solution to detached valves is the stick on ones available from all good kite suppliers.