Sorry but you won't be able to access the Pitt River without boat. The Upper Pitt River drains the back side of Whistler area( Garibaldy Mtn Range)into Pitt Lake, the lake is about 14 miles long then drains into Lower Pitt River ( no fish) then into Fraser River which eventually drains into the ocean.
There is a old logging road on the north end of the lake that travels along side the upper river and there is an active logging operation on that road. To get there you need a boat to travel across the lake, then you need a bike or hike up the road. The river is a wild river so there is not much room to walk the shore, there is a few access points at 5km, 12km and 20 km but I would not walk or bike that road with a shot gun, lots of bears up there.
You won't find anyone to take you up there on the cheap as it is an expensive trip to run a jet boat up the river, not only that but very technical and dangerous so you don't want to go with someone who is not experienced at running that river.
Your best bet is to hire a guide for one day and enjoy the trip. If you are looking to fish rivers without a guide, try Vedder, Chehalis, Skagit, Coquihala river.
Lot of pics of the Pitt on our website - Fishing in British Columbia - STS Guiding Service: Flyfishing Photo Gallery