Xen: use case: force guest type (PV or HVM)

I have a running Centos x64 Dom0/Cloudmin gpl/ configuration, which is running fine.
However, i noticed that 32bit DomUs will be created as HVM, 64bit DomUs as PV.

This is done automatically, and i could not find the relevant setting to override that in cloudmin.

My goal is to be able to force the guest type definition (PV/HVM) when creating a new DomU.

Any help is appreciated.

Many thanks