Timber frame infill over cavity wall/steel lintels

[lookseehear]

Looking for some assistance with a detail:

 

Need to infill above this window on gable end (lintels are steel beams on inner and outer leaves). The builder doesn't want to use masonry because it won't tie into the steel and he thinks it's just going to end up unsafe. He suggested timber frame, but I guess it would need to be strapped down, which is again problematic over the window.

 

If we go with a timber frame, do you think straps either side of the steel would be sufficient? Timber frame just on the outer leaf? or on both?

 

Any alternative ideas?

[markc]

Ties welded to top of beams or bent strap ties bolted or shot nailed onto top of beam will tie the blockwork in. 

[lookseehear]

Thanks - I like this idea. I assume I'd need to get the SE to confirm it's OK before we start drilling holes in the top flange, or am I OK if the holes are small and not drilled in the web?

[Russell griffiths]

Twin stud wall, full fill with rockwool type insulation, take the insulation down between the steels also. 
long straps from 3 courses of blockwork down to timber studs. 
thar ridge beam will need a fair bit of insulation around it too.