Making ProxyPassMatch work with Location in apache2

I have recently created a configuration where apache2 proxies requests to pentaho running on a tomcat backend. The first problem I faced with the ProxyPassMatch directive is to do with the way the url pointing to the backend is written. Specifically, using a url that includes a non standard port like 8080 may result in a ProxyPass Unable to parse URL error. I fortunately found a workaround for that bug on the apache bug list.

When ProxyPassMatch is enclosed in Location - the first argument - which is a regex pattern, is left out. It is used as an argument to the Location directive instead.

The url provided to the enclosed ProxyPassMatch should be combined with the expected result from regex pattern. This is done using $n where n is count of parenthesized matches starting at number 1.
If the parenthesized matche(s) are not provided to the url argument of ProxyPassMatch, the whole matching string will be concatenated with that url and this may result in an unintended path.

Example

<Location ~ ^/(pentaho.*)$>
    Order Allow,Deny
    Allow from All
    ProxyPassMatch ajp://127.0.0.1:8329/$1
</Location>