you need to contact the long-arm quilter you want to quilt your quilt and see what she would like- it might not be a problem- but a fix-easier than taking anything apart would be to just add a lightweight muslin (or other interfacing) to the whole top when it is completed-would not have to be fusable- could just be basted onto the back as a stablizer.
but check with the quilter to see- different quilters are going to have different fixes= and some will not quilt t-shirt quilts no matter what you use....it's all a personal thing...if you have a quilter who is experienced quilting tshirt quilts she may not need you to do anything- or have the perfect (fix)