So, I've managed to install slack32 on slack64 chroot - this allows me to avoid having multi-lib system. In this setup, connecting using ssh locally will provide the chroot environment as normal user. I've successfully built mingw cross compiler using this setup.
However, I just found out that I can't do su here, which gives me a problem of not being able to run slackbuild scripts. I almost went crazy after looking at it for a couple of hours before noticing the obvious - just manually chroot into it!
I just thought I should jot this down in case I have to go through this again... and only because the slackbuild script I'm running is still not done :-)