lzw-compressing the data then base-64 to armor it might give you 1.5:1 on stuff over 1KB or so. I ran into trouble with Javascript getting clever about bytes an

lzw-compressing the data then base-64 to armor it might give you 1.5:1 on stuff over 1KB or so. I ran into trouble with Javascript getting clever about bytes and Unicode characters. But, yeah, some efficient compressor and then an efficient url-safe encoding might do it.