Pass a multi value argument to a panel view
The entity context provided by CTools uses tokens to provide keywords for the given context.

So if you implement your own token which uses a node object as data source it will end up among your node context keywords, and you can pass it to the view as an argument. 

Check out this answer to get an idea how to implement tokens.

Your token replacement method should extract the referenced node IDs from the loaded node, and concatenate '+' or ',' between them (it depends on how your argument is configured in the view).