Most of the problem is the mass of pipe, which results in it's inertia stressing the header/exhaust junction.
Soft mount the pipe at the pipe's CG.
Make an intermediate joint by cutting the header as short as reasonable and adding an additional silicon coupler at that point. You should be able to get a 3 to 6 inch piece of intermediate pipe.
The pipe will still wiggle around a lot, but the additional coupling will reduce the inertia transmitted to the header/exhaust joint.