I don't know the answer to your question, except that I've seen working memory discussed with regard to adhd.
I have a ds7 who "looks" like he has attention issues (difficulty paying attention) and also dyslexia-type issues (language processing problem - difficulty with reading comprehension and making inferences, among other things - along with history of speech delay and SPD/possible auditory processing issues). However, he does NOT have a problem with working memory, at least according to his most recent WISC results - working memory was his highest section LOL. He does have a significantly slow processing speed. My latest attempt to work on the attention angle includes nutritional supplements - I was looking into vitamin and mineral deficiencies related to adhd and came up with magnesium, zinc and B6. So far, they seem to help some aspects (e.g., getting dressed with no reminders instead of 8,000 reminders) but not others (he's still very "bouncy" - needs to move, quite dramatically sometimes, in order to think). Sometimes it seems as though there's a switch that needs to be flipped in his brain so that the energy going to his body can be re-routed to his brain LOL, and I just need to figure out how to do that. In testing, his psych also noticed the attention issue but we haven't gotten around to pursuing it further yet. That was a few months ago; I think the nutritional supplements are helping enough, for the moment.
The trouble with adhd is that other issues may look like adhd but aren't. There ought to be a list somewhere of other things to rule out - the Eides' book would be a good start though it's been awhile since I looked in it.
