My customers want me to deliver a solution that allows asymmetrical path's with SharePoint. I know this is not officially supported from Microsoft, but it seems like a reasonable request.
I'm trying to shorten my URL paths for country domains. This is a common technique used for Search Engine Optimization.
True, asymmetrical paths aren't supported by SharePoint. The best supported option is configure alternate access mappings.
I don't know enough about ISA or other proxy options but I would have thought this route is your best option. As long as its thoroughly tested this should work OK.
Update: There's also a programmatic option I came across: ASP.NET 3.5 SP1 routing with SharePoint 2007. However I'd be very careful about whether this is supported by Microsoft.
Also there is a lot you can do with other SEO techniques. I think you already know all this but for other people some good resources are: