Yes. I'm planning to do the same thing. I've got the parts in a box I just can't find the time to do it. You need to purchase an idler pulley and bracket to mount where the power steering pump once was. This was a pretty rare configuration so you might have trouble finding it at a junk yard. I purchased mine new from Mazdaspeed and it cost around $50.
Click here to view the 1991-1992 Mazda Miata Parts Catalog 1 of 3: Engine. Go to page 41 of 87 (1-G5) and look at assembly 15-970. That is the idler pulley. Everything that is outlined is included with p/n BP01-15-930.
My understanding is that you use the same belt as if you still had power steering but instead of the belt wrapping around a heavy power steering pump it just goes around a light weight idler pulley instead.