[XeTeX] How to mix math fonts?

[Mojca Miklavec]

Hello,

I would like to know how I can use unicode-math package for mixing
multiple fonts. (I don't mean taking a few characters from one font
and a few symbols from the other.) I would like to display one
character from LM Math for example and the same one in XITS math next
to each other, looping over "the whole" unicode range.

I could use \setmathfont for each individual character, but then it
takes ages to compile.

Thank you,
    Mojca