Aunt Annie, several people apply the glue by first diluting it, then using a small painter's tray and a sponge roller -- just like painting a wall, but smaller and with glue! Keep in mind that every square inch does not need to be covered with glue. Think more like basting with safety pins. You just need a little bit of glue every few inches to keep the quilt basted. If you leave large gobs of glue, these can become hard spots for your machine needle to get through.
Edit: I have arthritis in my hands and would never try to use a spray bottle to baste with glue. In my experience, repetitive stress of this type aggravates arthritis.