This is a really challenging question but Answers has always amazed me in the past.

One of my favourite guitarists, Vini Reilly (Durutti Column) for a
long time used a custom sunburst strat (1969). It had a washburn
wonderbar (2001) trem. It also appears to have a replacement for the
traditional five(/three)-way pickup selector switch which appears to
be a fixed mixer/selector switch which let's all three pickups be
balanced.

If anyone can find out what this product is, I'd be absolutely intrigued.

Thanks

Tom