While you could use a touch of 'Seal-All':
Amazon.com: Seal-All, 3/4 oz: Home Improvement - I've found that simply scuffing up the surface of the (stock) intake works quite well, giving the nylon[?] shim something to grip on. Another (untested) method would be to make an additional shim to compensate for any excessive play - a strip of aluminum from a soda can outa work
TBH I think the spacer/shim provides an excellent opportunity for additional product development, as we all know the intake port is already far larger than the manifold it's fed by and while the CNS venturi isn't huge - it's larger than the ID of the typical aluminum manifold, given the additional thickness of it's walls to maintain structural integrity.
The shim itself looks as if it's needed for that very reason, that the CNS was designed with a larger OD & ID aluminum manifold in mind - the spacer provided only to accommodate the thin-walled steel manifold. While the custom aftermarket billet aluminum manifolds provide an additional performance increase due to it's short & direct path - it's hampered somewhat by it's reduced ID, necessitated by it's material.
Given the CNS is now a stock item included with the new Grubee engines - I think it's time someone developed a manifold to take advantage of it's greater capacity & ridding ourselves of the gdang spacer entirely, it should be possible to have an aluminum manifold with at least the same ID as the steel ones given the extra space provided
