I'm on a double-entry TR visa and the first 60+30 days are expiring tomorrow, on the 9th. My problem is that I am going to Cambodia for a few days next week, so I am wondering if it's possible for me to make a visa-run

tomorrow and not use my second entry but instead get the 15 visa-free days that I would normally get if I did not have a visa? Obviously I would instead use the second entry when I return from Cambodia.

I have a feeling this won't work, but I thought it was worth at least asking if somebody knows. And no, I can't go to Cambodia earlier (or later for that matter).

Thanks

You can ask but most recent reports have been that it has not been allowed without canceling the visa entry. What you can do is obtain a re-entry permit for your Cambodian visit prior to leaving (1,000 baht) and that will keep your new 60 day stay alive and allow the 30 day extension of stay. Your visa expiration date has not passed I hope? Full 60+30 normally exceeds the 3 month period a visa issued locally is valid for.