ProxyTimeout using mod_rewrite proxy?

Hi.  Hopefully this isn't too off-scope for this list.  We want to implement the ProxyTimeout directive with the proxy facilities of mod_rewrite, not mod_proxy.  We wish to have:

RewriteRule ^/http/(.*)  http://$1  [P]
RewriteRule ^/https/(.*) https://$1 [P]

but including a 60 second proxy timeout on these due to an unreliable app server at the proxied destination.  Is this in anyway possible?

Many thanks, Nick.