I'm not entirely clear on what you're trying to do, but it seems to me all you need is something like:
$fields->addFieldToTab("Root.Content.Portfolio Pages", new DropdownField('PortfolioPageOneID", "Portfolio Page One"));
// etc..
And then you'd have all your accessors available:
$this->PortfolioPageOne();
$this->PortfolioPageTwo();
etc..
Looks like you removed the post, though.. so maybe that won't help. :)