proxypass only https

[Michael Ni <michaelcni@xxxxxxxxx>]

anyone know how can i do a 

ProxyPass     /foo/        http://foo.bar.com

but only where protocol is http and not https?


so
http://www.apache.org/foo/     would proxy to      http://foo.bar.com

but https://www.apache.org/foo/ would be denied

i looked at ProxyPassMatch, but it didn't seem right.