I don't know where you going to code this batch exec code but can you do this?
if within sql then
declare @execstatementsbatch nvarchar(max)
select @execstatementsbatch = ''
SELECT @execstatementsbatch = @execstatementsbatch + 'EXEC UpdateQty ' + ItemCode + ', ' + QtyBO + '; '
INNER JOIN .....
this isn't optimized way due to dynamic query i suppose, plus you have 4000/8000 char limit
if you going to execute your batch from front end
then you can build your batch in similar fashion as above (it will be quicker there)
i've seen somewhere on forums similar kind of code you mentioned in your first post
of directly selecting params into exec statement
not able to find it now
will keep you updated if i find it