There is DBIpp that is a Pure Perl DBI, which is almost
as fast as the C/XS version of DBI. You can check the
dbiusers archives for an actual quote of testing numbers.
There is also a Pure Perl DBD::mysql driver. These Pure
Perl versions would be easy to ship, 'C' compiling. Not
that this would be used for your product, there is also
the dbish which gives a Oracle sqlplus type interface
to a db, it will work with any driver(DBD::?) installed.
Check out dbish on search.cpan.org. There is one being
developed outside of DBI, which will eventually be part
of the DBI dist, that has more features. The DBIpp and
DBD::SQLite could be shipped with the product, although
I don't remember if DBD::SQLite is pure perl , you can
also check out DBD::AnyData.