There is no way within Numbers, it's all or nothing as you found out.
If it's something you'll do often you might want to use Applescript with these instructions.
And here's the script to do it. Open the Numbers document to the correct sheet before running the script.
set {ATID_run, AppleScript's text item delimiters} to {AppleScript's text item delimiters, ","}
tell application "Numbers"
tell active sheet of front document
set fileName to name
tell table 1
set aText to {}
repeat with aRow in rows
set aLine to {}
repeat with aCell in aRow's cells
if value of aCell is not missing value then
-- quotes added in case the cell value includes the text separator itself
set end of aLine to "\"" & formatted value of aCell & "\""
-- or
-- set end of aLine to value of "\"" & value of aCell & "\""
else
set end of aLine to ""
end if
end repeat
set end of aText to aLine
end repeat
end tell
end tell
end tell
tell application "TextEdit"
activate
set aCSVDocument to make new document at the front with properties {name:fileName}
repeat with aLine in aText
make new paragraph at after last paragraph of text of aCSVDocument with data (aLine as string) & return
end repeat
end tell
-- the document needs to be manually saved
set AppleScript's text item delimiters to ATID_run
