I'm having a similar issue (if I understood your question), as far as I know, drools allows only 1 start node per ruleflow, so the only chance I see to start a ruleflow at an arbitrary node is to start right into a gateway (diverge) node, the gateway node should be connected to every node in the ruleflow (or as much as you neeed), the rules defined for it should allow you to start the workflow at any node. Sure this work arround is not pretty but might be enough.
By the way, If you find a better solution please let me know.
Fuanka