Patches to BitCoinJ are always welcome :-)

If you'd rather do your own thing, you could experiment with writing a proxy that sits in front of bitcoind and multiplexes connections. Gavin is concerned about socket exhaustion as users move to lightweight clients. Multiplexing proxies are a battle-tested technique for reducing the strain of this type of thing. BitCoinJ uses thread-per-connection so wouldn't do a good job of that right now, but allowing it to use a mix of async io and multi-threading would be a nice improvement. It'd need some changes to bitcoind as well for a really good effort, to allow for IPs to be forwarded. I'm happy to discuss it more with you over on the bitcoinj list if wanted.