Hi Tom,
I haven't tried with shellac, but I know that it works well with sanding sealer. Do not use water based sanding sealer for this, use any of the fast drying sealers, those will have the characteristics you need for this. Use is in the similar way as you use CA, with the lathe turning pour the sanding sealer (about the size/volume of a small pea) on to a paper towel folded strip, gently take it to the spinning blank and with a light touch, rub the sealer 4 times (left, right) not too fast or too slow, about a second each way or so!
Let it dry (keep the lathe running) for about 4-5 minutes, then use either fine sand paper or fine steel wool for the first sanding, proceed with a touch with the last 2 or 3 grits you normally use for finishing. Clean any dust and proceed with your normal CA finish method/procedure.
I do a lot of work with pines, these are the steps I take, they have never caused me any problems, hope you get the same results...!:biggrin:
Cheers
George