If you can afford the inconstant speed (which I doubt since it's spec'ed
to 3 digits after the .) then the 'kludge' is the cheapest and best way.
btw this will induce some vibration that may have to be removed
mechanically. Do not treat it lightly, I speak from experience ;)

If you want real precision, determine the biggest common divider of your
frequency resolutions and aim for a clock of that frequency. This may yeld
a weird frequency and you may have to use a PLL or a custom crystal to get
near what you want. I understand that you want +/- 0.5 Hz, you will not
get away without a custom crystal or ceramic resonator imho, unless there
is a suitable frequency in the system that can be divided or PLLed to.

Did you know that it takes a crystal oven to achieve +/- 0.5 Hz and that it
can only be maintained over short periods of time (minutes, at most hours
with very high quality components after a good burn-in of a few weeks) ?

hope this helps,

        Peter