Slide saddle rails for stoker all the way forward. Also, saddle clamp fitting on a beam can be moved fore and aft on the beam itself (loosen the two small allen bolts at bottom of clamp and tap clamp fitting with block of wood/hammer), although that could present an issue with proper positioning.
Best solution: find an extra long adjustable stoker stem; Co-Motion has those and Burley may have that in stock. It will bring the bars several centimeters closer to the stoker.
Hope this helps!
Pedal on TWOgether!
Rudy and Kay/Zonatandem