I have used all kinds of things for quilt backs, including poly and microfiber. I am also a fan of glue basting! Here's what I do in these cases when the top is cotton and the back is not. I lay the back down wrong side up, put the glue on the back and place the top right side up on the glue. I use an iron to help set the glue, but since it isn't advisable to put the iron to poly, I always iron on the quilt top side. I learned this lesson the hard way when I ironed some fabric that was actually 80% cotton and 20% poly and it melted the edges. As long as you set the glue (I use liquid for this) with the iron from the top it will still work on poly or microfiber. But iron just enough to set the glue so there is not too much heat applied to the poly back.