linux mysql server 5.1 optimization with more than 160 000 databases (free hosting) on one server

I need very good expert to optimize my mysql server futher. Somebody who already worked in the enviroment with huge number of databaseses on one server - currently 160 000. You cannot run standard optimization scripts, because they will crash the server - going through every file on 160 000 databases would take days and slow down the server so it won't be able to serve normal content. So you need to careful to not put too much load (especially durning peak time) when checking everything. My problem is that mysqld process only takes 10-15% of memory, so this DB depends on system cache, which i think is not best for DB. i would prefer this mysql to use more RAM , but if i raise some values too much, i think i have stability issues. (even though not even 50% of ram is taken by mysql) anyway - somebody needs to carefully investigate the situation and try to optimize all [login to view URL] values, so the server can better use it's RAM.