umm its late and i might not be thinking straight but...
he is applying for tier 2 and not ilr as you mentioned it in ur original post
ILR, as we know it, might not be there in Oct 2011. rumours are around that it will be replaced by something similar, but different nevertherless, in summer of 2011. just so you know.. i dont know if this changes anything or not...
Basically contact UKBA, ask for advice whether you should change your COS or are they willing to give him visa that would take him past 5 years period.
its immigration law, its bound to be complicated and confusing:)
regards