Breeding out White Markings or making a PEW self

I am working with Siamese genes (codes Siamese and Himalayan) in my dual purpose colony. One of the annoying challenges is that you pretty much cannot buy Siamese selfs (solid color); nearly all of them carry hh hooded or Hh berkshire. Selfs aren't too hard to eventually get because Siamese babies show their markings in their first coat. A few test breedings with the berks that came out of the last litter and I'll have my siamese selfs.

Here's the real toughie: Himalayan rats (One copy siamese (ch) one copy albino (c)) are white as babies and so are PEWs so they mask white markings. How can I achieve an unmarked (HH) Himalayan or albino? I need to figure out what test crosses I can use if any. The point of breeding out white markings is to allow color points on the feet to show up. The obvious answer would be to get a known pedigree PEW or Himalayan but good luck finding that without driving several hours to a show breeder...

All I can think of right now is to keep a pure Siamese self strain and pairing them to albinos when I want Himalayans, but never breed the Himalayans themselves. I'm willing to do some lengthy outcrosses; all the culls feed snakes so it's not a waste. Just means I need to be patient about getting the colors I want.