I've implemented a process with the sender creating a semaphore before sending a file request so that the receivers can use it - that all seems to work! :)
Next issue...with our NDM implementation the sending and receiving IDs are different. My receiver processes are running under the receiver ID and can't remove the semaphore created by the sending ID when they're complete, even though both IDs are in the same group and the semaphore has group read/write permission. Is there an IPC semaphore permission that allows deletion by other than the owner?