RPSL route-set/as-set query.

Hi Colleagues, I had a question that I am unable to find an answer for within the RPSL RFC's, it seems that it is not possible to nest route-set objects within as-set objects, would this be a limitation of the RIPE DBM, RPSL or syntax ?! The reason I ask is that we are migrating a customer onto our network and whilst renumbering we will be advertising there assigned blocks from another provider. We currently use as-set's to depict our announcements to peers/providers so would like to add these to our as-set using a route-set object without having to replace our as-set object with a route-set object for our peer/provider announcements. Thanks, Adam