I have not seen any documented mods for that.
Are the TM751s new? reason I asked is the newer ones have a different receiver board in them and maybe labeled differently.
Date Code on the little white sticker usually on the back may help.
It should not be too hard to find the resistor used to drive the SCR trigger signal and clip it.
I see that hawk1 gave you the link to one of the modification sites. I don't believe there is one for the TM751 but there is a schematic of the one before the new RF board. On that one R18 220 Ohms is the SCR Trigger drive to the SCR and in theory [never tried it] should stop the SCR driving the switch if cut. While R19 and C17 will keep the SCR from noise tripping it.
I will try later today to look at a newer one and maybe test my theory.
Dave beat me to an answer and his is also a very good way to go. Now you have a choice.