How about appender.put() with var args?

[Justin Whear via Digitalmars-d]

Appender will take a range, so you can also do:
  app.put(["foo", var, "bar"]);
 
or
  app.put(chain("foo", var, "bar"));

But yes, a variadic put would be convenient so long as it wasn't 
ambiguous in some way.