In Gmail, multiple contacts are separated by commas. If I needed to send an email to recipients
andrewW@gmail.com, bigStackuser@gmail.com, firstname.lastname@example.org
I would write them exactly as such in the "To" text field. The method allows for any number of contacts, according to Google.
This method also works with names on your contacts list. If your contacts contained a "John Smith" and a "Babe Ruth", then
John Smith, Babe Ruth,
would be valid. Bear in mind that names not followed by commas will not be valid unless the name is confirmed by the user via selecting from the recommended names that normally appear when typing recipient names. This includes names that come at the end of a list of names separated by commas. This question is addressed in "Sending to a Group of People" at Gmail Help.
The problem is that when contacts are pasted into the "to" text field, they do not contain an email address. The reason that verified recipients are grayed out is in Gmail is because they contain hidden text. The element for a verified recipient contains this code:
<input name="to" type="hidden" value="Mr. Test <mrTest@gmail.com>">
Double clicking on a verified (gray) recipient reveals the true text:
Mr Test <mrTest@gmail.com>
Essentially, this means the only way to paste a recipient is with an email address, or a name and an email address. This is probably so that emails aren't sent to duplicate names, as Google allows you to store multiple contacts of the same name to a single account.
I know that this doesn't solve your problem to the parameters that you asked for, but I can think of two alternate solutions.
Create a contact group in Gmail. But I assume that this group is dynamic, which is why they need to be copied from a list.
A better solution may be: Add the email address next to the names on the list you are copying from in
Name <emailAddress@gmail.com> format. (This format does not require the use of commas.)