Yep, Hippo hands absolutely.
As far as the pressure, there is a way to snake a piece of welding rod or a thin piece of aluminum into them so that they hold their position and stay out and in front of the levers.
A lot of it depends entirely on what temperatures we are talking about; there is a huge difference between riding at 40F and 25 F and what works at 40 F often will just not work at all at 25 F.
Brian
I couldn't use mittens, heck I dislike insulated gloves. Hippo hands work great, but be aware, wind pressure will cause them to put pressure on the clutch and brake levers. Another thing is Baker hand wings or similar. Find some silk glove liners, warm, thin, and easy to wear. If you don't mind insulated gloves there are some ski gloves that have a pocket on the backside for hand warmers.