I recommend packing a pair of hiking boots to save your feet. When you're only a few miles from your car, it doesn't matter too much if your feet get wet fording streams or stepping in mud.
I have only exited Rocky Basin this way in the spring, so I must write my description here as such, a descent. However, next time I go to the peak, I believe I'll ascend this way.
Once in the gut of this north-fork drainage of Mueller Park Canyon (Rocky Basin), I would ascend the prominent ridge on skier's right of the Session's Peak Run
. It would be steep enough that booting may be required. Mind the avalanche conditions on the final push to the summit.
That said, once you've skied Session's Peak Run
, continue skiing down the drainage until you find the horse corral. Doing so, you may need to traverse the west side of the drainage more often than skiing right down the center of it to avoid a splash in the stream. Don't ski until the drainage confluences with the main Mueller Park drainage. What you're looking for is the Kenny Creek Trail, or signs of it, as it's likely all covered in snow.
Once you think you've spotted it, or the general area, skin or boot west to the top of the ridge. From here, you can ski again, even if only for a little bit, but it's worth it. Find another stream and follow it up the mountain. It's likely the Kenny Creek Trail overrun with melt-water. This suspicion is confirmed by the occasional pop-can bottom you'll find nailed to a tree. You'll know you're on the right track if you find the remnants of an old cabin long since destroyed.
From here, the trail is easier to follow, especially once you get below the snow-line. Just keep going and the trail dumps you out on the Mueller Park canyon road.
Before reaching the horse corral, take note of all the juicy terrain on the east side of the drainage, and across the canyon.