Keeping Part of a Failed Match Without Consuming Tokens

My Lua grammar currently cannot handle function definitions whose parameter list ends in the var arg operator, like this one:

function foo(x, y, ...) print("hello") end

The relevant terminals are parameterList and identifierList:

parameterList.production = identifierList + (@comma + @varArgOperator).Optional()
identifierList.production = @identifier + (@comma + @identifier).ZeroOrMore()

When parsing inside the identifierList production hits the var arg operator, it terminates unsuccessfully because it's not an identifier.

I tried using this CanMatchCallback for identifierList:

private bool CanMatchIdentifierList(IParserState state)
{
  var tokenReader = state.TokenReader;
  tokenReader.Push();
  try
  {
    if (tokenReader.LookAheadToken.Id != LuaTokenId.Identifier)
    {
     return false;
    }
    tokenReader.Advance();
    while (tokenReader.LookAheadToken.Id == LuaTokenId.Comma)
    {
      tokenReader.Advance();
      if (tokenReader.LookAheadToken.Id != LuaTokenId.Identifier)
      {
        return false;
      }
      else
      {
        tokenReader.Advance();
      }
    }
  }
  finally
  {
  tokenReader.Pop();
  }
  return true;
}

However, that results in no identifierList match at all, not a partial one up to the comma before the var arg operator.

I also tried using an OnError callback that returns the Ignore result. When I advance the token reader inside of it, parsing is successful, but the var arg operator is passed over entirely. If I only return the Ignore result, I still get no identifierList match.

How do I correctly handle this scenario so that the parameterList match goes up until the last comma before the var arg operator when it's present?