Scratch

I read the post by johnm about concurrency from 2007:

http://scratch.mit.edu/forums/viewtopic.php?id=8130
johnm said: "It [Scratch] runs as many commands as it can until it gets to the end of the innermost loop. If it doesn't hit a loop, Scratch simply runs the rest of the blocks in the stack."

MY QUESTION is if there's a way to force a script (or a portion of a script) to run through without being interrupted?  -assuming that it DOES have loops.

So for example, say I have ten sprites, and each one has a script that includes loops.  I'd like each script to run through completely before the next script is executed.

I could put each script in a forever loop and have a wait until [it's my turn] at the top.  The script whose turn it is would run for a while and then execution would go to the other scripts but would quickly return to the desired one.  This doesn't seem ideal.

Or I could put each script under a unique "when I receive" block.  Then some other script could "broadcast and wait" each unique message in sequence.  But I want all ten scripts to run many times per second - so I'm not sure if the broadcast method is best.

I will test these two options, but I'm hoping there's a trick to force a section of a script (including loops) to run all way through.

Thank you for any help you can give me.
Jeff