If the handle has some flex to it, my solution would be to use micarta or some other "tough" synthetic for the scales......just make sure the insides of the scales are flat, then do a couple "spot" anneals, drill, and use something like Loveless bolts. Once you glue, the clamping pressure of the Loveless bolts, combined with the strength of the micarta or G10 will "flatten" the tang. Let it cure out and finish out the handle.
I've repaired a number of blades over the years that had this issue (a warped tang), and as long as there is some flex in the tang, you can accomplish the method I described fairly easily. A word of caution..... the method WILL NOT work with wood/natural handle material...at least not for very long. Any natural material won't handle the stress, and will either separate at spots along the tang, or crack/break.