Are you absolutely certain about this? Have you consulted an accountant?
The reason I ask is the following: http://arcweb.sos.state.or.us/pages/rules/oars_100/oar_150/150_314.html
Specifically 150–314–0429 (1):
“(1) For purposes of ORS 314.665 and the rules thereunder, “tangible personal property” means personal property that can be seen, weighed, measured, felt, or touched, or that is in any other manner perceptible to the senses. “Tangible personal property” includes electricity, water, gas, steam, and prewritten computer software.”
Computer software should be treated as “tangible personal property”, and if it does, then it should be taxed the same as an Oregon Retailer would.