Well, that's quite easy: Add this directive just outside your mod_cluster enabled VirtualHost:
CreateBalancers: 1
Check out what it does: CreateBalancers docs. Furthermore, create a proxypass.conf in your conf.d/ with, e.g., this content:
ProxyPassMatch ^/documentation/ !
ProxyPass / balancer://mycluster stickysession=JSESSIONID|jsessionid nofailover=on
ProxyPassReverse / balancer://mycluster
ProxyPreserveHost on
If you experience any problems with cookies, try to play with: ProxyPassReverseCookie* directives.
The aforementioned snippet simply says: if it's /documentation/, don't forward it to the workers and serve it locally.
Lat but not least, where is your EnableMCPMReceive directive? What version of mod_cluster is it? I stongly suggest against using anything older than 1.2.0, and I recommend using the latest 1.2.6 version. Absence of EnableMCPMReceive implies a very old mod_cluster without a crucial security fix...
HTH
Karm