As Simon has said - Timbermate is a filler. Generally Timbermate will take stain (i.e., if you fill holes with a wood coloured Timbermate, then stain it, the Timbermate will stain as well), is easy to apply and clean up (just use water), can be thinned down to a wash (with water) and is fairly versatile. It can also be reinforced with CA glue (good 'ol superglue) to give it some strength - e.g., if you're using it as a fill in a fretboard.

An option for a fretless hollowbody is to get a standard hollowbody, then remove frets. Couple of ways to fill the gaps - if you want to get rid of the lines, you can use some similar coloured timber veneer, or to keep them, plant pot labels are the right size to leave small white lines. It can be done!