Brother 1nickt thanks for the hint and the pointers to SQL::Abstract which helped me to put together the literal SQL queries below:

my %where = (
    '(roles &2) => \'(roles &4)',
);
[download]

and

my %where = (
    0 => {'<' => \"(roles & 4)"},
);
[download]

or

my %where = (
    '(roles & 4)' => {'>' => '0'},
);
[download]

bw, bliako