R: space taken by a row & compressed data

> We have an FAQ item about this.

Damn! I didn't see that one! Sorry...

> Long data values are automatically compressed.

The reason I'm asking is:
we have a system that stores 200,000,000 rows per month
(other tables store 10,000,000 rows per month)
Every row has 400 columns of integers + 2 columns (date+integer) as index.

Our system compresses rows before writing them to a binary file on disk.
Data don't usually need to be updated/removed.
We usually access all columns of a row (hence compression on a per-row basis
makes sense).

Is there any way to compress data on a per-row basis? Maybe with
a User-Defined type?