This configuration makes a sticky loadbalancer with 3 backend servers. It is not dependant on any specific configuration of the backend server such as JSESSIONID or PHPSESSIONID.
It will create a BALANCEID-cookie with a route to a backend server.

#You need at least these modules

#Header used for setting cookie

LoadModule headers_module ...

#Proxy

LoadModule proxy_module ...

LoadModule proxy_http_module ...

LoadModule proxy_balancer_module ...

#Set a cookie if BALANCER_ROUTE_CHANGED containing BALANCER_WORKER_ROUTE environment variable
Header add Set-Cookie "BALANCEID=hej.%{BALANCER_WORKER_ROUTE}e; path=/;" env=BALANCER_ROUTE_CHANGED

#Show balancer-manager
<Location /balancer-manager>
  SetHandler balancer-manager
  Order allow,deny
  Allow from all
</Location>

ProxyRequests Off

#Configure members for cluster
<Proxy balancer://jakeri>
  BalancerMember http://b1.jakeri.net:80 route=server1
  BalancerMember http://b2.jakeri.net:80 route=server2
  BalancerMember http://b3.jakeri.net:80 route=server3
</Proxy>

#Do not proxy balancer-manager
ProxyPass /balancer-manager !

#The actual ProxyPass
ProxyPass / balancer://jakeri/ stickysession=BALANCEID nofailover=Off

#Do not forget ProxyPassReverse for redirects
ProxyPassReverse / http://b1.jakeri.net/
ProxyPassReverse / http://b2.jakeri.net/
ProxyPassReverse / http://b3.jakeri.net/

I believe that this configuration is somewhat better compared to this guide.

I got to fix my css for the <code></code> :-/