I just flew my kit-built 4*40 for the first time today. A whole lot faster than my LT-40 trainer! I used the OS 46FX from the trainer instead of using a new motor, thinking that I knew it was reliable and would keep "new motor" problems from causing a crash. To make a long story short I ran it out of fuel on a takeoff about 50' off the ground, and got to test my dead-stick ability on the new plane on the first day. Couldn't make the runway but got it turned around and level, and floated it into the grass in the field without any damage!
But back to the subject at hand... I carved away a little bit of the motor mount diagonal webbing as suggested above and also loaded the cable end with solder to stiffen it up. Seems to work just fine- and I was able to use the hardware provided with the kit without another trip to the hobby store!