Pass the hash as a reference instead of using %hash, and on the line where it assigns the $ptr->{$key} = {} add something like "unless ref($ptr->{$key}) eq 'HASH'" or something.. that will probably wipe out any existing values you put in there though.. e.g.:

builder(\%test, 'abc', 1, 2);     # $test{1}{2} = 'abc'
builder(\%test, 'def', 1, 2, 3);  # $test{1}{2} is now a hashref, not 
+'abc'
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