Get all %artist% values from a list of files and put them into %album artist%?

How can I do that? I am trying to make an action to get all artists from a split album (eg. Artist1 & Artist2) into the Album Artist field (as in 'Artist1; Artist2)
I know the $meta_sep function is only for a file and not for a list of files, so I couldn't do it with it. I tried exporting a txt file with a list of the artist names just once and import it to Album Artist with seperation but I can't get the output to be the name of each artist just once.

Is there a way to do what I want? Thanks for the help.

What do you want to achieve with such a string content, ...
for example ... for 12 tracks ....

'Artist1; Artist2; Artist3; Artist4; Artist5; Artist4; Artist3; Artist1; Artist6; Artist7; Artist1; Artist2'

in the ALBUMARTIST tag-field?

Wouldn't it be better to fill the ALBUMARTIST tag-field with 'Various Artists'?

DD.20130127.1838.CET

If it's a split album by 2 artists, I would want the ALBUMARTIST field to be "Artist1; Artist 2" so that in foobar they appear under both artists. If the ALBUMARTIST field is 'Various Artists' then for each Artist only their respective tracks from the split will appear for them in my library. I hope what I am trying to say is coherent.
Thanks a lot for the reply!

Note that foobar displays a multi-value tag-field as 'Artist1; Artist 2'.
Use the dialog "Extended tags..." from Mp3tag and check how the tag-field ALBUMARTIST is stored.

If you want to create a multi-value tag-field within a list of files with Mp3tag, ...
... then select the files,
... open the dialog "Extended tags..."
... create two tag-fields ALBUMARTIST, each with one unique artist name.

Check it out how it looks in foobar.

DD.20130127.1907.CET

That works indeed! Is there a way to automate it with an action though? I'm trying to organise the tags of my whole library.

Find inspiration there ...
Listing all Artists from Album into One Tag Field

DD.20130210.1700.CET