Surprised they slide down. Will give you a tip. The nose piece on of the Hypermask is likely the same design as the Sportmask....rubber molded over an inner metal insert. This gives the nose piece tremendous adjustment and memory which to me is really what separates the Rudy from Oakley, Oakley being just a solid rubber nose piece that can't be adjusted. Based upon the bridge of your nose and all of ours are different, sometimes radically, you should be able to get the Hypermask to stay put if you adjust the nose piece. You have many options. If you turn in the two lower tabs of the nosepiece they will dig more into the side of your nose and create a more solid connection.
Since I don't like the feel of doing this, I do something a bit different. I turn out the extreme bottom of the nose bridge but keep the upper part of the inverted U a bit closer together. This reduces any digging of the ends of the nose piece and yet creates a solid connection. Again, the nose piece has great adjustability to keep your Hypermask in place. You may want to experiment a bit.
Thanks for your input.
PS: a further tip about adjusting the nose piece. The best technique is with a pair of needle nose pliers. Grasp the side of the nose piece you want to bend with the pliers 'next to where you want to bend it' and then use your index finger to bend the nose piece to desired shape. This takes all stress off the nose piece to lens connection which you don't want to disrupt. HTH.