I think over the past summer or two, my aluminum wheels (18" Mille Miglia Evo5) have seen enough bumps that they're starting to deform. The two on the passenger side are 'off' enough that they're vibrating the car at speed.

I don't suppose aluminum wheels can be repaired, can they? (They're 1-piece gravity-cast, if that matters.)

I've resorted to using my stock wheels for now. It'd be nice to salvage that investment. :(

Any ideas?

Yes, wheels can be repaired of refurbished. I ran across this when I was looking to have mine repainted. One place that I remember is Ketstone Automotive but there are several others. If I recall correctly, a completely refurbed OEM wheel was about $150 after the core refund. Repairs will vary due to the type of wheel and severity of the damage.

Do a Google search for wheel remanufacturing and sift through all of them.