I do not think a linear pol. filter can damage anything. It is not the sensor that has a problem with linear polarizers, but the AF method used. The AF can not determine focus when all polarized light is removed. A circular polirizer lets light with different directions through, allowing the AF to "see". Same goes with film SLR's.
So, you can use a linear polarizer on your Pentax. Just not with AF, as you already noted.
Canon EOS 350D, Tamron SP AF 90mm F/2.8 macro, Sigma 18-50mm F2.8 DC EX, Canon EF 70-200mm f/4 L USM, Tokina AT-X124 Pro 12-24mm F4, Soligor 1.7x C/D4 DG Teleconvertor, Manfrotto 724B tripod, Canon Powershot S30