It's both feasible and permissible - just hike up the main trails to the top of the summit lift. As you approach the top lift station, to your left (the uphill side) look for a foot trail headed steeply up the bank. It's almost directly across from the start of Skyward. There used to be a sign for access to The Slides, but I don't know if it's still there. Anyway, find that foot trail and it leads you all the way up to a junction with the trail coming in from Whiteface Landing and then on to the summit. It's easier to find coming off the summit than coming up the ski trails, but it's there.