You do not need MNPS approval to fly above MNPS airspace. If you can reach FL420 or above then you can climb or descend through MNPS - known as special dispensation for aircraft not approved for MNPS.
As previously stated this would still be a problem it ATC coverage is limited.
Icelandic AIP 1.8.3.26 (
http://www.caa.is/media/PDF/ENR.pdf)
OR
http://www.worldairops.com/NAT/docs/...AirOps.com.pdf
section 1.5