Вы очень близки, но вот правильный сценарий.
tell application "Finder" to duplicate "somefile.txt" of (container of (path to me)) to applications folder
tell application "Finder"
set prevTIDs to Applescript's text item delimiters
set Applescript's text item delimiters to ":"
duplicate "somefile.txt" of (text items 1 thru -2 of (path to me as string)) as alias to applications folder
set Applescript's text item delimiters to prevTIDs
end tell