Hi vlad; Welcome to the forum. There's no "good" way to do it without adding another switch, but there is a way to do it, if you don't mind a compromise of the #4 notch position. You'ld end up with:
1. neck
2. neck and middle (normal parallel)
3. middle
4. middle
5. middle and bridge in series.
This would work with a standard 5-way, you'ld just have a duplicate of the middle-only position.
I can post a diagram tomorrow, if you'ld like. (Just finished a 10-hour day. I'm pooped tonight.)
Artie