And yes, unfortunately, you will have to take care of quoting the data yourself.
...that's half the point of my question, and being forced to use 'generate' defeats the benefit of using SQL::Abstract.
Nonetheless, thanks. I'd glossed over the generate function in the first place, and the following is sufficient for simple inserts:
my $dbh = DBI->Connect(@params); # initialized elsewhere
my $sqlgen = SQL::Abstract->new;
my %data = (a => undef, b => 1, c => q/'string and string'/);
$_ = $dbh->quote($_) for values %data;
print scalar $sqlgen->generate('insert into',\'atable',\%data);
INSERT INTO atable SET a = NULL, b = '1', c = '\'string and string\''
(Not sure whether the way it's quoting might cause trouble with, e.g., ZIP codes, where '08540' <> 8540...)
Still interested in a broader solution.