Url Rewrite with a CMS - Dynamic Rewrite

Question

Hello,

I would like to change URL Rewrite working in the CMS of the company I'm working for

I have already done a little one:

eng/MyFolder/16/MyCategory.aspx

MyFolder/index.aspx?FolderId=19&LanguageId=1&SiteItemsCategory=16

with:

{R:2}/index.aspx?FolderId={Folder:{R:2}}&LanguageId={Language:{R:1}}&ItemsCategory={R:3}

I use rewritemaps for LanguageID and Folder

  <rewriteMaps>
    <rewriteMap name="Language">
      <add key="eng" value="1" />

        .
        .
        .

    </rewriteMap>
    <rewriteMap name="Folder">
      <add key="MyFolder" value="19" />

        .
        .
        .

    </rewriteMap>
  </rewriteMaps>

But for ItemsCategory, i have to take the category id (16) send in the URL.

I want to take off the number (16) in my URL to have something like:

http://localhost/eng/MyFolder/MyCategory.aspx

The things is, a CMS User can add a category if he wants

So i can't put "MyCategory" and his "id" in rewritemap

because the user don't have to touch to the Web.config.

How can i do it well?

Thanks