1. create your latex frame, and include your bibliography stuff at the end of the document as you would for a normal document. i.e.
2. Find out what the current temporary filename scribus is using for rendering is. It will be mentioned in the 'Program Messages' listing. The file will be in the $TEMP directory.
3. Jump into that directory and copy your bib file into the $TEMP directory.
4. Run bibtex on the temporary filename.
5. Run latex again, and again, using the 'Update' button on the Editor dialogue.