You're right: reading again my post, I find it quite cryptic myself... sorry.
The idea is the following:

@sorted_keys=sort
 { fmt($hash{$a}->{oid}) <=> fmt($hash{$b}->{oid}) }
 keys %hash;
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where fmt is defined as above (with the correction in split below, sure!). You can also use cmp instead of <=>, if you wish.