Ignore serialization of default values

Hi,
I'm serializing a big amount of data.
My serialized strings are getting huge, double digits of MBs, because the serialization save my default values (Null in my case) of each record.

Is there a way to have the serialization and ignore those empty values and populate them with the default values from the record on the de-serializations.

I tried to overwrite the handlers on my own, but if i'm not mistaken - i cannot overwrite handlers for record since its already have a handler of it's own.

So, is there a way to do so? To save only the fields that have actual values different then the defaults? It will reduce about 70% of my storage data.

Thanks