Swiss singer Stefanie Heinzmann has recorded the song "Ain't No Mountain High Enough" as a duet with Ronan for the Deluxe version of her new album "Roots To Grow", which is due to be released on Sept 11. You can listen to a short audio clip, and buy the song, on Amazon.

Update - Here's some additional links to online stores where you can purchase the track.
Musicload.de
7digital.de (this might work internationally if you pay via paypal)

Additional information