Is there some sort of splint (that actually works) that can hold the big toe away from the second toe?

Yes, but...: There are splints made to help hold the toe in a proper position. I often use these after surgery for a few months to protect the toe while it's healing. However, these splints themselves will not correct a bunion. Look at hapad.Com for a nighttime bunion regulator and a viscoelastic toe spacer.

Yes: Most of the splint are used at night and can be found in a catalog or drug store. During the day you can use a toe spacer. They will not correct the positon of the toe forever.