Okay, I have used install_name_tool in the way that you recommend and in XCode I have added a custom "Copy Files" build phase that copies the dylib to my Resources. Using otool on the binary in my application bundle reveals that it is now looking for @executable_path/<etc>, and checking my bundle reveals that my dylib does now turn up in the right place.
I therefore hope that I can just deploy the output of XCode without doing anything at the command line. I guess I'll find out!
EDIT: if anybody feels like testing, then I've uploaded to
here (~ 956 kB). It "should" be compatible with 10.2 and above, but I've only tested on 10.4. It's an OS X port of a BBC Micro emulator by Tom Walker, with native menus and so on. It runs kind of slow because of some of the libraries it depends upon but anything 1 Ghz ish should run the emulator at full speed. The real question is: does it load up and run?