Magento: attribute input type

Two attributes of the product of my project have more then 5000 items. I need to give the product one or more items of this attribute. If I use the type attribute "multiple select", the page is very slow and hard to find items, select and use ctrl. I need a new kind of attribute type that uses ajax: in the page, attribute must be a textfield and when the user types some characters the server should return the items with those charachters (such google search). When the user writes a new item, which is not in the database, it must be possible to create and assign new item. Must be able to delete the items assigned to the product.