GVA-HEL//HEL-GVA is also notorious difficult getting upgrades to.
I have never been able to use my vouchers on any of the segments between the two dep/arr destinations as they simply do not exists by the look of it... I always end up flying from ZRH to HEL (and return). This said, wasted on E-190's anyway (GVA/HEL) so not the end of the world!