I am an Ajarn in Muay Thai, National Champ amateur (retired after holding for 7 years) and now pro. I own a school and actually am holding a fight this weekend. I have taught karate boxing and kickboxing anbd wrestling. I am also the VP of the association that handles the sport. Thats my info incase you want to know who are the peeps giving you instructions.
Personally, Wing Tae followed by side clinch, add a slap knee to the sternem then a straight knee to the quad, eject the rusher with arms, leaving a jab out to keep % of retaliation to a minimum and add a Teep into hip area to fold him. That will end the rushing for the rest of the fight. Other option, though much less effective, is a Stab knee to rusher into front hip flexers orfloating rib into elbow if you cannot elbow, then in to clinch, spin 180 and eject with a low leg roundhouse to calf for takedown.
Side stepping and uppercutting wont work, and backing up is NOT an option. You also need to defeat them mentally too. These techniques are meant to do just that. They may carry a higher % of risk for you, but the payoff is far greater.
Im sure you will get many opinions, find the one that works best for you.
btw if knees are not permitted, then you arent doing muaythai, you are doing kickboxing. hehe! Just a side not.
If you need to subtract knees, I would suggest wing tae ( running sidestep about 6 inches off side of opponent into a round house hitting at the thigh level acrossed both thighs. then turn in 12 eject with arms and add push kick to pelvis area!!
Ajarn Army