Using graphviz "rank" feature with gt.graphviz_draw

Graphviz has a "rank" feature that allows nodes in a "subgraph" to be
displayed at the same level. I would like to use this (or another feature?)
to accomplish what I describe in the example below.

Example: In the attached image, the number drawn in the centre of the node
is its identifier. I assign a vertex property defining the hierarchical
level ("lvl") for each node as follows:

node 0; lvl = 0
node 1; lvl = 3
node 2; lvl = 2
node 3; lvl = 1
node 4; lvl = 0

I would like those nodes to be displayed at the same hierarchical level in
the image. E.g., nodes 0 and 4 both have lvl=0 and should be drawn at the
bottom of the image. Node 1 should stay at the top.

Note: the last example on the following page seems to show how to use
Graphviz to do what I want (although I would like to define the subgraphs
based on my lvl vertex property), but I am not sure how to implement this
through graph_tool. URL:

Or, perhaps there is a simpler way of doing what I want to do?

I don't think this is possible with graph-tool. Things like graphviz
subgraphs and vertex groupings are not supported... The only thing you
can do is to set the vertex positions by hand yourself.