There are two ways I can think of to achieve a similar effect. Let's use this example from the Django docs:

    info_dict = {
      'queryset': Poll.objects.all(),
    }
    (r'^(?P<object_id>\d+)/$', 'django.views.generic.list_detail.object_detail', info_dict),

One (pretty simple) solution would be to use a block to pull out the object in question:

    match "/:id" => object_detail {|params| Poll.find(params[:id]) }

Rails 3, with its ActiveRelation integration, could also support a syntax similar to the QuerySet syntax:

    match "/:id" => object_detail(Poll.all)

where Rails would internally take the Relation from Poll.all and do @relation.where(:id => params[:id]). To be honest, while the newly available syntax is nice, lightweight block syntax is pretty nice as well.