I'm a little unclear about what you mean by "too narrow to have a hub-centric lip," but the wheel spacers I use for two sets of wheels I have for my Spec Miata don't have a lip.
I have a set of gunmetal Team Dynamics wheels and a set of Kosei K1's that don't have the right offset, so I use spacers. I torque my wheels to 85 foot-pounds, and I've not had any trouble (knock wood).
The one pictured below is roughly the same as the spacers I use. This one looks thicker than mine, but the design is the same.