Yeah, the bits of the Challenge that aren’t the normal trail are the footpath at the top and some bits run in the opposite way to normal, so not really accessible for you at during a weekend. Generally what’s in the forest is either fire road or the MTB trails, there’s not very much other stuff unless you leave the forest.
If you do the South Loop climb, when you get to the top you can hack through some undergrowth in the direction of Grisedale Pike onto the ridge and up onto the summit. From the top, right and onto Hobcarton End is a great descent back into Whinlatter, or you can go straight and bear left down to Coledale Hause, then left again into Coledale and Braithwaite. This is proper awesome rock descent. If you want more, head up Newlands as far as Stonethwaite, turn right up the old mining track, then right onto the top of Barrow. The descent off Barrow back to Braithwaite is really fast and fun.
HTH.