I would imagine that if you wrapped your other database package so it worked like DBI then you could do that. What other database package are you hoping to use? DBI is the central module for nearly all perl database interactions and in general it is foolhardy to use RDBMSes without using DBI.
You should seriously consider migrating off of Sybase::DBlib, as DB-Library is being phased out by Sybase (no new functionality, etc.) Sybase::CTlib, Sybase::Simple and of course DBI/DBD::Sybase are the modules to use so that the underlying access method used is Sybase's Client Library.