I don’t think this will work reliably, unfortunately. There are a few issues. The voltage drop across the ESC could vary as the thruster speed changes, which could cause one ESC to see a high voltage and the other to see a low voltage. Also, the signal and signal ground connection for the high-side ESC would be at 20-25v, so if you connected it to a Thruster Commander or other signal source it would burn it out.
If you only have a 40v power source, the best solution would be to use a switching regulator to convert that to a lower voltage. Here’s a power converter that would convert 40v to 12v. This converter has enough current output to handle two T200 thrusters. At 12v the thruster will have reduced power output compared the normally recommended 16v.
The best solution is to use a different power supply!
Hope that helps.