Standard operational crew for the Hudson was usually 4 and often included a crew member designated as 'second pilot' . If you google "Lockheed Hudson" and "second pilot" you'll see it mentioned frequently. This was obviously an advantage for Coastal Command and RAAF Hudsons where longer distances on patrol were flown. The books RAAF Hudson story Parts one and two mention second pilots as crew members often and there's also a mention here:
http://www.epibreren.com/ww2/raf/269_squadron.html
269 was one of the early RAF Hudson units. As can be seen from the losses, the crew carried normally was 4. The most common breakdown for crew tasks I've seen was as follows: Pilot, Second Pilot/Navigator/Bomb Aimer, Wireless Operator, Gunner.
So the standard issue was one multitasker per plane
As to how the issue of a second pilot was handled an indication is given in here:
http://press-files.anu.edu.au/downlo.../pdf/ch161.pdf
which looks at the crash of Hudson A16-97
Quote:
Settling into the cockpit of Hudson A16-97, Bob Hitchcock, his small suitcase
stowed, was secure in a dual-purpose harness. His ‘QC (quick connection)
seat type’ parachute allowed for interchangeability with the second pilot or navigator
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So cockpit gymnastics were the order of the day if a pilot needed to be relieved/replaced.
As mentioned dual controls were available for the Hudson and used for training purposes.
http://www.adf-serials.com.au/2a16.htm
is a list of RAAF Hudsons in which can be noted a number of the early serials had dual controls and were rushed into combat due to the need for aircraft. However you can also find notations for aircraft having the dual controls removed [A16-11, A16-15, A16-17].