$ perl -MO=Deparse -e '$$hash{"key1"}{"$var2"} = $value'
$hash->{'key1'}{"$var2"} = $value;
-e syntax OK

$ perl -MO=Deparse -e '$$hash->{"key1"}->{"$var2"} = $value'
$$hash->{'key1'}{"$var2"} = $value;
-e syntax OK