Who decided that Sally Hansen Hard as Nails was the official substitute for commercial head cement ??
It's highly likely that some outdoor writer mentioned it in an article somewhere in the past, it took hold & many of us have been using it ever since. That's as likely as anything!
I use Sally Hansen's & epoxy most. Also use Tear Mender, super glues & some other common adhesives found in craft shops or hardware stores. Haven't used commercially produced head cements in many years.
For super glues, there are those that are very thin, and if care is not taken, it's possible to ruin a fly, as that thin glue has a tendency to wick into anything porous it contacts. Learned that lesson the hard way. Use it sparingly. The gel types have their place too.
For the original question, some of the fabric paints can also be used to form a hump on a fly. There are many with various consistencies & many, many colors. I used some in the past that dried clear, so it did look like a bubble. Have used some that were very thick & held there shape very well.
Not a adhesive, but transparent glass beads, the type that have a silver colored inner lining can also be used to get a similar effect. They can be coated with anything you want that is clear, or left as is. Thread a piece of cheap, clear monofilament through the beads then secure with your tying thread. I don't recall the exact technique, but it involved tying with the beads & dubbing the body around the beads. Quite a few years ago, there was a tier who was doing this. Gives the appearance of air bubbles attached to a nymph. I think I read about it in Fly Tyer magazine. Glass beads also add a bit of weight, and is not a bad idea for those concerned about using lead wire.
Another possible method is to use hot glue. There are mini glue guns that output precise amounts of the glue that could be used to form such small bubbles. There was a fellow who did this & formed the bodies on hooks for Bonefish flies. The glue sticks are available in many colors, including some that have glitters in them.