Yep, Dexxyy's bang on.
DPDT
1 6
2 5
3 4
1 = solo switch 1 (from board layout)
2 = solo switch 2 (from board layout)
3 = nuthin
4 = "normal" LED cathode (negative leg)
5 = ground
6 = "solo" LED cathode (negative leg)
As Dexxyy described, run power to a 2k2 resistor (or other value, depending on how bright you want your LEDs). Connect the 2k2 resistor to both the "Solo" LED anode (positive leg) and "Normal" LED anode.
You've got the right idea for sure to take it slow and triple check everything. The G2D is ambitious, but completely doable as a 3rd project as long as you're patient and careful. It also sounds fantastic, so it'll be worth the effort (and then some!).
Good luck!
Q: Why is a drummer like a scud missile?
A: Both are offensive and inaccurate.