In the top file, you can provide a 'node-hint', which is similar to a
'fix-node' in that it specifies a starting mapping for the virtual
node. Unlike a fixed node, however, assign is allowed to move hinted
nodes around all it wants.

Add a '-t' option to assign that allows you to give a starting
temperature, instead of going through the usual melting process.

Together, these may be helpful with the pre-pass we're planning on
incorporating into assign. During that pass, assign will be working
on a coarsened version of the virtual graph, so there may be some
places where decisions are made poorly due to the reduced information.
After one run has been done with the coarsened version, we can run
assign again with the full version of the graph, but with 'node-hints'
that start virtual nodes where the first run decided. This will allow
assign to fine-tune the results of the first mapping.

Of course, we don't want this second run to take too long, so we'll
want to start it with a low initial temperature (so that it basically
just does hill-climbing), and probably use a fractional '-H' argument
to prevent it from spending too long on large topologies.