RewriteRule to pass key=value parameters to ProxyPass

Hi team,

Apache mod_proxy ProxyPass supports multiple key=value parameters.
RewriteRule with [P] flag causes the request to be handled by mod_proxy. Is
there a way in RewriteRule to pass some key=value to mod_proxy ProxyPass?

eg: ProxyPass can transparently support websocket via upgrade=websocket

ProxyPass "/foo/" "http://backend/foo/" upgrade=websocket

But below doesn't seem to work:

RewriteRule "^/foo/(.*)" "http://backend/foo/$1" [P, upgrade=websocket]

Any ideas?

Thanks!
Frank