Not possible I`m afraid. You need DTV-RADIO a an alarm source, but it`s not in Beotime. But why not set a timer in BV7´s timer menu. Does work with my BV7-40. Set DTV-RADIO and number as alarm timer source and set the BL3500 to timer on.
Or get the century to the bedroom. Beotime also works with BS Century (my daughter sometimes uses the Beotime as a wake up timer for her Century).
The only workaround I can imagine is a Lintronic box. Set Beotime to Radio as alarm source and the Lintronic box will receive this command and send the needed command(s) to BL3500 - expensive solution.
Stefan