Like the new plank
If you keep your centre fin but add a strake that runs from somewhere halfway back on the root chord to the fin LE AND run the elevons in to the root, when you apply a roll input the lateral shift in the centre of pressure gives the fin an apparent angle of attack and thus a positive yaw interaction.
The dear old Vulcan had such a feature...
Also, as a bonus, the strake adds useful strength.
(not getting any flying OR building done atm)