Before i understood that Prop was what actual caused the pain i only thought that Test Prop was painful (based solely on bro lore). I thought i would be fine cutting it with any oil based injectable to soothe it. So i was ending up my first cycle of test e with the same idea as you and i loaded up 1 cc/100mg test prop, 1 cc/100 mg mast prop in the same tube (thinking the mast would ease the pain). Shot it in the quad. Holy fukking shit, i couldn't bend my knee for a week. Those quads aren't about to stretch after that.
After a week or so the pain does subside but 2 props are going to hurt period. The only thing i've ever been able to do that actually worked was to cut with ethyl oleate. You can buy it as a sterile oil in a vial. Its actually pretty thin so it has the impact of thinning too. Draw your prop blend, then draw 1 cc ethyl oleate. On top of that i'll sometimes run the tube under a blow dryer and really thin out the oil before shooting.
Remember, no matter how thin you get the oil, still shoot it SLOW.