have you tried/heard of the I-205 bike path? It crosses the Springwater corridor and goes up north along I-205 all the way to the Glen Jackson.
If you're going towards Gresham on the Springwater, you'll cross Bell Ave, stay on the path and you'll reach the I-205 bike path crossing within about a mile. Turn left there and it should take you to Vancouver.
Now, I've never used this route, just heard of it, so not sure if there's anything wrong with it.
I managed to find one decent map that shows where it's at.
Good luck and be safe