Thank you for contacting us regarding your pre-order unique in-game items. Unfortunately you can not add more than one pre-order Access Key to any particular account. If you want to get the other item, you could first log into your current beta account during the next Beta Weekend Event and click the Edit Account button on the bottom left portion of the character selection screen to change your email address to another email address. This will free that email address up to be used to create your new Beta pre-order account with in-game item that you want. At, launch make sure to activate the correct pre-order beta account to retail status.
Please let us know if you have any other questions.
Regards,
The Guild Wars Support Team
If I read it right in order have two pre-oreder items you need two seperate e-mails, bit this way you can have 8 chars

Ren