Create fictional glasses that have a refractive index of 1, done by setting a0 in the Schott dispersion equation to 1.0 and the rest of the terms to zero.  Set the wavelength range to 1E-9 and 1E+9. Set the density and TCE to whatever the spacer metal is. Name it "aluminum", "titanium", "SS-304", etc.  Create a "METALS" library for your new glasses.

Using these fictional metal glasses in the LDE will enable Zemax to draw the spacers, and model mass and thermal dimensions properly. 

Thanks for the tip Mike!