Very easy to do, it's just not something that most "Jemsiters" would do.
One way is to simply screw a couple of "stoppers" under the springs so that the trem block has something to come to rest on. (Check out "All about Evo on vai.com, the 'Back-stop' will give you an idea of what I'm talking about)
Another way is to cut and shape a block of wood to use as a stopper between the guitar body and the trem block, basically the same thing, but you'll get more wood to bridge contact (some say you get better tone and sustain this way) but it's much more work.
I had someone that wanted just this same mod with an OFR and I just used two wood screws and a set of straight metal braces (set it up like a solid back-stop, no up, just down) and it worked fine.
I hated it myself, no up, of course, and no flutter, plus if I forgot about it and just let the bar go after a 'wiggle' you get a loud "CLUNK" from the bridge as it hits the brace . . .
Not something many of us would do to our guitars, but Van Halen has had his guitars set up for no up, just down from the "Franken-Strat" days, so whatever works for you.