Creating a paravirtual EC2 instance from CloudFormation script

I try to launch a t1.micro EC2 instance via cloudformation script. The AMI is paravirtual (Red Hat, x86_64, paravirtual). My script fails with the error "failed to satisfy constraint - use a valid EC2 type " . Amazon still supports the previous generation instance types, such as T1, C1, M1, and M2 that do not support Linux HVM AMIs but the paravirtual AMIs. Indeed I was able to create manually the required t1.micro + PV AMI . However it seems that this is not possible via cloudformation. Do I need to set any additional field for using previous generation instances in cloudformation scripts?