The day use fee is if you go into Paso Picacho camp ground. You can avoid the fee if you can figure out where else to park your car, but you can't park anywhere along the road near the trail head like you can in the southern areas of the park.
If you're up for some extra hiking, you can park at mile 7.3 on CA-79 and walk up the Cold Stream trail, parallel to the highway, until you hit the main Stonewall trail. This is an extra 1.8 miles each way.