You can use Select dynamic for Name of customer and set it to use database table of your first content type to load options, if your storage is standard - article, this would be #__cck_store_form_YOURCONTENTYPENAME, if not see bellow tutorial for info which table you need to look at
there is a certain limit regarding number of options, when this search option is activated, I think this is set to 10 by default. If you have more than 10 options it should work.
I'm uderstand your need. We can do that by devoloping a new "CCK Field Plugin". This plugin can use a javascript animation like that "http://jqueryui.com/autocomplete/".
If you want, we can develop this plugin for you during a support session. Just let us know.