you could use GE 100% silicone sealant. I have used it to glue lifter patches on a tarp-tent.
However, it will be a lot heavier than just sewing it and if you are joining silcoated and uncoated it may not stick well to the uncoated fabric.
If you can make a pattern and cut it out you can easily sew it together vs. gluing. I think you would be much happier with something sewn vs. glued.