You might want to make a gradual transition to SCD and slowly get your child used to some of the foods. Gradually practice the syringe method until you are ready to start the diet.
Some parents use a turkey baster to do the syringe method.
I would use the syringe to gently place (rather than shoot) liquid into his mouth. This allowed him to (a) get used to tastes without textures, (b) have more of a feeling of control, (c) spit it out if he really couldn't cope.
More tips from me...
For safety, parents should make sure the food is not too hot. Lukewarm/room temp is best for syringed food.
Also for safety, nothing thick should be shot toward a child's throat. Preferably, liquid is also introduced at the entrance or middle of the mouth. Swallowing is an activity that starts from the front of the mouth and works progressively backward. It is also naturally but carefully coordinated with breathing. It can be extremely frightening, not to mention life-threatening, to have a blob of food (even puree or thick broth) or liquid enter your eating tract at the back of the mouth or throat.
Before using it, make the syringe feel unthreatening: Let the child hold and play with it. Give him a second syringe to hold/play with throughout. Take turns --let him syringe stuff into your mouth, too!
Have the food in a bowl, with a spoon in it, within his reach, to maintain the association and in case he decides he'd like to try that.
Maximize the benefits: Syringe broths properly prepared from bones (not just meat) and high mineral, well cooked vegetables. Include the oil from bone or meat/fish broths. Include high quality sea salt.
I like the turkey baster idea better than the syringe. Too bad I didn't think of that in time for my son! :)