Can't always have what we want, unfortunately.
It's been a frustration "for since forever" that there's inconsistent and limited support for LaTeX/TeX in MATLAB -- there's just enough to entice but to almost always frustrate if try anything but the most basic either way.
There simply isn't any known way to do what you're asking for; you can write the fraction w/ LaTeX and accept the available font or use a chosen font with TeX and try to kludge up a text expression, but you're wasting your time trying to do anything different; just can't be done...
Heaven only knows how much time users have spent on such attempts....
