You might want to consider the Michell reflex clamp. It's light weight and you have the option of using it in reflex mode. It's supplied with a felt washer that you place on the spindle under the record. You clamp down with enough force to help flatten the record.
I have both Michell and Sota reflex clamps, but I rarely use them in reflex mode. Either will work to hold the record in place. The Michell is a bit shallower so extra tall spindles could be a problem. I doubt if that applies to Thorens, but I'm not sure.
http://www.michell-engineering.co.uk/accessories/record-clamp/
I have both Michell and Sota reflex clamps, but I rarely use them in reflex mode. Either will work to hold the record in place. The Michell is a bit shallower so extra tall spindles could be a problem. I doubt if that applies to Thorens, but I'm not sure.
http://www.michell-engineering.co.uk/accessories/record-clamp/