Reduce g++ RAM usage

I haven't really found a solid answer to this question other than "get more ram". Is there a way to reduce the memory used by g++ during the compile process? I am (for reasons) trying to compile webkitgtk on a g4 mac mini with 1GB ram. It can't be upgraded. Current compilation options are -Os -mabi=altivec -mcpu=native -mtune=native. It has 1GB ram and 1GB swap but just runs out of memory. While I could theoretically just keep adding swap space, in practice this gets very slow, and I want to minimize that.