instead of naruto using the frog sage fusing to his shoulder couldn't he just make shadow clones to absorb the natural energy and tranfer it to him. remember this
so if thats the case if one of his clones achieves sage mode then he should as well when the clone releases and have multiple clones stationed around him so when the natural energy supply from one clone is exhausted another clone can release and send him it's natural energy supply.
and if your question is how would the other clones knowhe needs more? create a clone knowing he needs more energy make it release and then the other clones will know because the knowledge will be spread among them.
And you ask how will each clone know when is it its turn to release? naruto will simpily have each clone on standby wait for the clone before it to release
(and yes I was bored when I thought of this)