Whatever problems you have aren't "Perl string max string length" problems.

    my  $long_winded_string = "This is a weighty argument, though a bi
+t light on the reasoning" x 1_048_576;
    printf "How long is it?  %d characters\n", length( $long_winded_st
+ring );
__DATA__
How long is it?  66060288 characters
[download]

You may indeed be having problems convincing Sybase to take your large BLOBs (hint)

Update: I went looking (Google) and found this mention from the "Programming the Perl DBI" book, in "Appendix B. Driver and Database Characteristics":

LongReadLen and LongTrunkOk attributes have no effect. The default limit for TEXT/IMAGE data is 32 KB, but this can be changed by the SET TEXTSIZE Transact-SQL command.