Can persistent image be forced to sync ONLY on shutdown?

Hi.

I'm hoping to use a Knoppix liveCD with the "toram" and persistence cheatcodes to enable my laptop to only need to power the CPU/RAM for improved battery life.

Currently, it seems, after rebooting with myconfig=/dev/sda1/****.img and myhome=/dev/sda1/***.img ..that my home is mounted as read/write, and changes are written to disk fairly often.

Is it possible to make it ONLY write/sync to the harddisk (***.img) during shutdown to avoid spinning up my hard drive for periodic writes?

I'd assume it would have to be made to read the img and mount it as ReadOnly then use the UnionFS to make it seem writeable, then remount it r/w at shutdown, then commit/flush/sync/write the changes to the **.img file then?

Any information would be very helpful. Thanks for your time in advance!