I have used flar, but only a few times. It's quite neat, I think. To be honest, I only ever used it with tapes, but I'm sure that there's a splitting facility.
While I look to see if it's obvious, I have to point out that I encountered a few bugs with it that prevented me from restoring from it. Unfortunately, the only one I can remember right now is one where if /var/yp doesn't exist on your master machine, then restores will completely hang, so the flar is unusable.
You can try using flar -s after you've created it to split it, but it doesn't seem to have an option to set the size, so it may not be what you're looking for. As per usual, Sun's documentation is not exactly the best.
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Bitt Faulk