You could write a loop in prontoscript which called the dimming function the required number of times. If you know prontoscript, that would be easy (but why would you then be asking?). If you don't know prontoscript, the 'ton of commands' option is by far the easiest. Note that, depending on your 'electrical environment', either option might be a bit problematic in that they both assume that all the X10 dim commands are successfully processed.

I have heard that, with certain lamp modules, one can use 'direct dim' X10 commands (effectively "dim to X%") but I have never got these to work myself.