Had a thought on this one in the car this morning... This is not very elegant but it would work - just might need more regular maintenance of the flow content.
Schedule the flow weekly on Mondays, then determine the dmedate, and add a branch at the beginning that compares the current date to the dates you want to run on... (You would just need to add dates in the future but you could just reminder yourself to update the flow once a year with the new run dates.)
datenow =10/10/2011 || datenow =10/24/2011 || datenow =11/7/2011 || datenow =11/21/2011 || datenow =12/5/2011 || datenow =12/19/2011 || datenow =1/2/2012 || datenow =1/16/2012 || datenow =1/30/2012 || datenow =2/13/2012 || datenow =2/27/2012 || datenow =3/12/2012 || datenow =3/26/2012 || datenow =4/9/2012