I took a manilla file folder and cut it the size of the unfinished fabric used for signing. Then I cut out the area to be used for signatures. On the inner back you can use a Sharpie to draw a baseline for those who need it. The just place the fabric into the adjusted file folder.
I found it is easiest if there is a one on one for the signatures: the designated helper with the Pigma pen and then the signee. Otherwise it can get messy and your pens can somehow walk off.