My skin-on-frame kayak that I built currently does have anything at either the bow or stern. Ultimately I intend to do something for purposes of being towed and whatnot.
But, for now - any idea on how to use bow & stern lines without having toggles/carry handles/deck rigging?
Same problem
I have the same problem with a Struer touring kayak that has no fittings at either bow or stern. My solution was to install Kayakpro EZ-Vees - these cradles are long enough that the tie-down can be done to the cradle instead of the boat. In your situation, I would just install some nylon webbing or some sort of fitting to attach the lines - why wait?
Painters
May not be what you have in mind but the simplest thing and what I do with the boats I build is drill a hole through the gunwales and thread a line through, tie it off and make a painter. There are lots of options once you get the line through. Oh, just seal around the line with some Lexel of maybe silicon caulking. If you take you time it will barely be noticable.
I prefer to do this before I skin but I have forgotten and had to add a couple afterward.
Just wrap it around?
I forgot what you built and what your vehicle is, but my own SOF extends a couple of feet fore and aft of my [short] vehicle and I just wrap the bow and stern tie downs at the ends. They serve the primary purpose to stabilize the kayak just fine this way.
Of course, if it was to slide off the rack or with the rack off the car’s top somehow these would not be of much help. But the probability of that to happen has got to be pretty low.