...do it yourself. In this case, fortunately there's an SL resident out there who knows how to do it.
Check out SH-2761. Alison Alena has gone to the trouble of analyzing the default SL avatar mesh, and has made some improvements in it. The JIRA entry (and Penny Patton's blog post about it, which is how I heard about it; many thanks, Penny!) describes how to set things up so your SL client will use the improved avatar mesh. (In brief: back up the "character" directory under the directory your client is installed in, then unzip avatar_lim.zip into the character directory.)
If you look, you'll see the JIRA entry is assigned to Charlar Linden, and fix version is listed as "Sprint 33". Of course, we all remember what happened to the JIRA entry to let mesh clothing adapt to non-skeletal shape parameters, but maybe this change really will go into the official client. We can hope, and in the meantime we can take advantage of it ourselves.