As far as I know there is no way for a pilot to create a DME arc in the FMGS using the MCDU - if it's in the database then you can use it, great, otherwise as you rightly say, create a series of points - painful.
However, you can do it manually: Display the arc using FIX INFO (1L - 1R FIX INFO - Navaid - Radius if your FMGS is the same as the A320). Select TRK/FPA on the FCU (again, assuming it is the same as the A320) then steer the aircraft around the corner.