Would prefer you to buy more licenses of course :-).........but the answer to your question is yes, you can have multiple databases on the same machine.
Keep in mind you should create on a separate instance, with different admin users, groups, etc., when creating different databases (not a must, but makes admin easier).
If you have a DB2 license for a CPU, you won't get charged double of you have more then one database on that CPU.
On the Partitioning side, if you are working on a DB2 Datawarehouse, and it will eventually grow into the 100s GBs and even TBs......then it is always an idea to look at DB2 Partitioning (DPF Feature).
Graham Martin
http://www.ibm.com/software/data/db2/migration/