Oh jesus..
Sigh..
Take all the stems out and the switch tops, put them in a bottle/jar with alcohol, and Gently shake them..
Take a cutip, wipe all the switch rails. Be very careful not to get the cotton caught on the leafspring, you might pull one out..
The main problem might be the stem hole...
Overall, do the best you can on removing what's visible inside the switch housing.
You don't need to worry about getting it 100% clean, a little lube is fine.