Use the same bib file for BibTex and BibLaTex

I am forced to use BibTex for my paper, because this is defined by the journal template. Till now, I used biblatex with the @online field for citing websites, which does not exist in bibtex. If I use the note-field for setting the url and date manually, this messes up my documents if compiled with biblatex. If I do not use the note-field, no url and date are displayed if compiled with bibtex, because this does not recognize these fields.

How can I use bibtex and biblatex for online references on the same bib-file without messing up the references?