Quick suggestion: Allow those annoying stones we're constantly mining out, to be used as single-shot (very likely to break on impact, to the applause of many), extremely short range (1 square distance across, unlimited z levels down, additional z levels meaning splattage), "thrown" (but more like dropped) weapons.
This would ofcourse require the nerfing of throwing in general. It might also be dangerous to the attacker (perhaps only if not wearing a helmet?), as well as the target, but what's an epidemic of skull fractures and brain trauma, compared to getting rid of masses of stones every seige?
This might be handled in a somewhat similar way to seige engines, except that the dwarf functions as the "engine", being assigned to the "drop rocks on hostiles" duty, and with the ammunition being the nearest rock pile.
This might also help allieve various seige improvement concerns, and nerf the difficulty of the early game slightly, since it would allow a player to quickly form an (atleast more) effective defensive force at the nearest elevated terrain, which players could in short time, and no doubt interestingly, improve.
Additionally, it would atleast make having tons of stones around that much more attractive, and hopefully pave the way for real "murderholes" and similar seige defensive tactics.
Balancing would be brought to the table by the fact that all these dwarf "engines" are still, well, dwarfs. Needy, greedy, attention-deficit, self-destructive, inaccurate and inconsistent weapons, in other words.