Matt Hinze draws attention to a little-known (translation: new to me) item in Appendix B of the TortoiseSVN documentation, Create a shortcut to a repository. In short:

Create a new shortcut and set the target to:

TortoiseProc.exe /command:repobrowser /path:"repositoryURL" /notempfile

Replace repositoryURL with the path in the desired repository. Thanks to Travis Illig for passing this along.