I had an idea for some gloves for the heavy a while ago but I never ended up fleshing it out. This reminds me a lot of my idea so I will try to finish it here. It definitely allows the heavy to become engineer's best friend.

The Hydraulic Hammers:

They are able to perform the same actions as an engineers wrench (AKA Build/Repair Buildings, Break Sappers, speed up build time, etc). Doesn't require metal

-10% movement speed while active
-15% health on wearer
-25% damage on impact
no random crits