BibTeX, biblatex and biber ⇒ Customizing BibTeX "Alpha" Labels

[Sadeq]

I use the bibliography style "Alpha" for BibTeX. It is vey good, but sometimes I like to override the label it gives to a citation. For example, look at this:

@inproceedings{br93,
Author={Mihir Bellare and Phillip Rogaway},
...
Year={1993}
}

BibTeX Alpha produces [BR93] as citation key, while I prefer something like [BeRo93]. According to http://nwalsh.com/tex/texhelp/bibtx-14.html, one can customize the label using BibTex field "key". But, "key" is used by BibTeX only when "the 'author' and 'editor' fields are missing."
Any suggestions?