You can unset multiple variables by separating them with spaces, not commas.
/unset %a %b %c
unsets %a and %b and %c
Or by using wildcards as described above.
/unset %a*
unsets %abc and %a and %a.bc
Also, you can use the $+ command without $eval-ing the result.
/unset %ab $+ c
unsets %abc
-genius_at_work
