Not knowing what you have in mind I am just going to jump in here with what comes to my mind.
If it is a "block" you want to put on the front;
I would make the pieced block.
Next, I would use iron on interfacing the size of the block on the underside of the t-shirt.
After pinning it in place (or maybe using a fusible), I would then quilt the block to the shirt. Maybe stitching in the ditch, or a 1/4" away from the seams in the block.
Would love to know what you end up doing.
I may try this on some sweat-shirts and tees to use for gifts.
Could use a golf, hunting, fishing, etc. for the guys.
Can you tell my mind is wandering?
Joyce