First of all, even if your don't take into account the bad news below, your regexp would not match what you are trying to match.
But now the real bad news: what you want to do is not possible because the '# portion' is not part of the request to the server. This '# portion' is a named anchor and will cause the browser to scroll to that anchor if it can find it in the document it requested.
If I take your example url:
the actual request sent to the server would be
GET /somethinghere/p-herealso/ HTTP/1.1
It is therefore not possible to take any rewrite action on the named anchor since the server does not know about it.