Building packages on different pc to target

I've just installed 4.0-beta on an Inspiron 3500 laptop but as yet 
there seems to be a lack of prebuilt packages. Due to lack of hdd 
space I've used remote nfs mounts for /usr/pkgsrc_distfiles and
/usr/pkgsrc and started building required packages which is a slow 
job. The server is NetBSD 3.1_RC1 and p4-2400 vs p2-366 of laptop. Is 
it possible to build for NetBSD 4.0 on a 3.1 system? (I'm guessing 
not but would feel even sillier if I didn't ask and it turned out to 
be possible)

David