Hidden dynamics are something I hadn't thought of.  Thanks for the suggestion!  They seem to work better, but still cause some issues with human playback.  For instance, I have a figure of a dotted quarter note + 4 32nds at mf, and of course the 32nd notes are almost inaudible.  If I add a hidden f dynamic for the 32nds, they are now played at a reasonable volume - but for some reason, the dotted quarter is now cut very short, as if it had a staccato mark.  So I added a hidden tenuto mark to the dotted quarter, and that seems to more or less do the trick.