Rescue corroded alloy nipples on wheel spokes, perhaps using chemicals? My wheelset has alloy nipples which have severely corroded.  It needs rebuilt with brass nipples.

However, my LBS can't get the spokes out.  The nipples are too disintegrated to turn, but not disintegrated enough to just crumble to dust and release the spokes.  

The LBS says the only option is to cut and replace the spokes.  This will be expensive (multiples of the cost of a simple rebuild using existing spokes).

My questions are:


Any suggestions how to get the spokes out?  
Specifically, are there any chemical tricks to accelerate the corrosion and entirely dissolve what remains of the nipples (without damaging the rims or spokes).


The wheelset has carbon rims, steel spokes, high-end straight-pull hubs, and alloy nipples.
In many other cases I'd apply heat (to the spoke) but I'd be wary of doing that here, because you could end up tempering part of the spoke, while it's still under stress. If you're unlucky that would lead to weakening. Also you don't want to get that much  heat too near the carbon rims. 

If you can get a few spokes right off, you may be able to slacken the wheel enough to flex the others and crack the bond (pliers on the nipples) or even to push the last few clear of the rim for more grip. This also means you can try different methods on different sections. 

You haven't said how much nipple is accessible, but with enough access you could file or dremel a slot (nearly) parallel to the spoke without going right through, then put a screwdriver in the slot and twist to split it. You'd need to split it over a decent amount of thread though. In my touring rims that would be possible. I suspect your rims are rather different, and they'd only need to be a little aero to deny you access to any thread.