on open myItem
    set APP_PATH to POSIX path of myItem as string
    set PLST to APP_PATH & "contents/info.plist"
    set MACOS to APP_PATH & "contents/MacOS/"
    do shell script "
    if [ -d \"" & APP_PATH & "\" ] ; then
        open \"" & MACOS & "\"\"`sed -ne '/CFBundleExecutable/{n;s/[[:blank:]]*<[^>]\\{1,\\}>//gp;q;}' \"" & PLST & "\"`\"
    fi
    "
end open

on run
    display dialog "Drop an application bundle on this to run it." buttons {"Ok"} default button 1
end usage

open bundle-runner in the applescript editor