You can use Dynamic DML to insert untyped SObjects one-at-a-time, but not as an array:

SObjectType token = Schema.getGlobalDescribe().get('contact');
SObject[] objs = new SObject[0];
for (integer i = 0; i<2; i++) {
  SObject tmp = token.newSObject();
  tmp.put('LastName', 'test' + i);
  objs.add(tmp);
  }

boolean showBug = true;

if (showBug) { // fails with "DML not allowed on abstract class SObject"
  insert objs;
  }
else { // works
  for (SObject i : objs) insert i;
  }