I guess what I would really like to find is a ticket agent with a reasonable markup. Agent prices seem quite high in San Francisco (double or more?).
Why don't you call Ticket Services directly and discuss your situation - they seem to be fairly flexible on exchanges. This links to some trio packages (elsewhere there's a warning about "demand based priciing" - don't know when that kicks in)
I'll have to keep an eye on Thursdays. Wednesday's curtain is earlier, so I think there are more commuters that night – and there are often Green Room interviews/lectures Weds before the performance.
Re demand-based pricing, it seems to kick in whenever. For instance I was in SF last April for two mixed programs, the price of which was the same on the day of the performance as it had been when tickets went on sale the previous November. But by that time, ticket prices for Cinderella, which was still 4 weeks in the future, and was already almost sold out, had doubled (yes, doubled!).