This is why I now buy dewaxed shellac flakes and mix my own. I can mix it to the cut I want and you have more options on colors (blond to garnet). It also accepts Transtint dye well to use as a toner. I usually use DNA to mix my own but I recently bought some 99% isopropyl alcohol to try because it is suppose to dry a little slower which makes it easier to apply.
A trick that I read about for dewaxing your own shellac is to put the mixed shellac in the freezer for a bit of time. This causes the wax to separate and congeal in the bottom of the container and you can pour off the rest of the shellac. Never tried it but it might be worth a try.
BTW, Minwax makes a sanding sealer specifically for polyurethane. I have have used it under their water based poly but not under their oil based poly or other brands like General Finishes. I have also used it by itself as a light finish on some turnings and by applying several coats it builds up and polishes nicely using a polishing wax.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.