Adhesive wouldn't be my first choice (far from it!), but try this method of fusing -- it works well for interfacings and might work here
1) Prepare your ironing board. Remove any of those metallized board covers and replace with plain cotton muslin, duck or canvas.
2) Prepare your press cloth. Dip plain muslin in water, and wring out by hand till the fabric is moist, not dripping.
3) Prepare the iron. For most household irons, set it to "dry" and "linen" (that is, no steam, high heat). Preheat for at least 5 minutes.
4) Place the t-shirt on the ironing board. Add the adhesive backed appliques. Cover with the wrung-out press cloth. Press (straight down, with force, not sliding back and forth in an ironing motion) for 15 seconds. Move the iron and press again until all the appliques have been pressed on. Press cloth should be dry but not charring.
5) Now comes the hard part: DO NOT MOVE THE T-SHIRT UNTIL IT IS COOL. No, cool, as in room temperature. Get your fingers off the edge of that applique. Cool. Completely cool. Ok, now you can try to lift the applique.
If the applique lifts, try again, increasing the dwell time of the iron in 5 second increments until it stays. If the polyester melts, try a cooler iron or a shorter dwell time. If the adhesive strikes through, choose another with a lesser amount of adhesive. The keys to fusing fabric are heat, steam, getting the fabric dry and then cooled without disturbing it. Household steam irons don't produce enough steam to do the job thoroughly, and the aluminized ironing board covers seem to keep the fabric both too wet and too hot for good fusing.
Kay (who thinks it'd be a lot easier to just do a corded raw-edge applique and call it done)