With the eCommerce Toolkit I think you will need to create a new add to cart or buy now button for this. Then you just need to have the option for the name or whatever the customization is. When you are setting up the item you can set a sample value for the option name and value. When you create the button and the form you can update it by changing the option value element to be a text field for the user to enter their name. Then when the user adds this item to the Paypal cart they will have the charge of the option and its value, the name entered into the text field.
If you get the extra option item setup like this and have any troubles with it please post back with a link so we can have a reference for the current configuration of it.