This is the method I used to create a weld line, I was actually just looking to fill a small joint between the rear of the tank and a new back panel I had made. While I was thinking of what to use, I carried on with the build and had to use some tamiya liquid thread lock,. Seeing its sticky consistancy and that it dries rock hard, I thought I'd give it a try.

Applying it along the seam, you can work on it while its drying.
Once dry, it can be painted.

This is quite a heavy line, but I'm sure smaller ones could be done.
Hey man....I just ride 'em, I dunno what makes 'em work.
Woof woof woof !