Request: Word Replacement Inside URL

Hello,

I would love a mod that would replace text within a URL with a predefined text string. For example, if someone hit the LINK button to insert a link and they put ftp://somesite.com/filename.zip, it would automatically replace that with http://somesite.com/files/filename.zip. 

Does that make sense? Essentially, word replacement within URLs. The native word replacement works if someone just straight types a link directly within a URL but it doesn't work when using the LINK button.

Is this possible? I recently took over a 3.1.2 forum and we just upgraded to 4.2.7 and that was definitely possible in 3.1.2, but not in the current version.

Thanks for your thoughts!