Do it permanently, get a small roll of Brownell's 'Force 44' low temp silver solder. ( the stuff that has the flux integral to it) You can work it easily with a propane torch and I assure you it WILL hold if you properly prepare the sight base.
I have used the stuff to resolder double ribs on an antique parker shotgun, replaced both modern and antique rifle sights and bases. JB has it's place, but in my opinion gunsmithing isn't one of them.........bedding material at best and even that can be done better with accra weld.
As an aside I have a friend that kept trying to JB a sight on a cut down Broomhandle Mauser, stuff would hold for a short period and then he'd be crawling around in the sand looking for the sight. I 'Force 44'd" the thing and he's been using it with no problem for the last three years.
By the way, the 'secret' to soldering is clean contact areas and the proper amount of heat...........dirty & it won't bond, too little heat and it will either not bond well or you'll have globs on your workpiece, too much and you'll likely not get it to work. Use just enough heat to get the solder to flow..........and really not much at all is required to have a really tough join. If you can very lightly tin the bonding surfaces.....you also will need some method of holding the two items in alignment, but you might have an easy go with a slotted base...........just don't use much solder................yeah, plumbers stuff will work but it lacks the tensile strength of the Brownell's product.............as I recall that solder is rated at close to 30M psi so it's pretty tough.
