I might be missing something here SR71, but here's my simplistic idea. If you start the turn 4 NM prior to the required inbound track at a speed of about 4 miles per minute, the turn will take about a minute. Thus, if you want to lose 1,000 feet during the manoeuvre, you need a ROD of about 1,000 feet per minute.
In practice, that will work out close enough IF you can achieve an average of 1,000 FPM descent through the turn without popping pax ear drums. I assume you're flying a pressurised aeroplane so there shouldn't be a problem as long as cabin diff doesn't get excessive.