Making CI's DBstuff play nice with slave/master setups

[eluser]moodh[/eluser]
Good evening!
I'm in the planning stages of a new project where we need to utilize a master/slave db-setup, and need some help with how to do this correctly.
My first thought was to simply set up two db groups, one to run selects on and the other to run insert/update/delete but seeing as the same sql statements always go towards the same server that should really not be necessary. Which leads me to extending/hacking the files in system/database as it's not extendable.

Is there a simpler way than to dive into the database-code or is that my only option?
Tips on how to actually do the fixing would be appriciated too, as I havn't started coding yet.

Thanks!