[iNik]

A couple ideas:

Set a "start date" and/or "Due Date" on your waiting task. That should keep it out of your perspective until such a time as you want to be reminded to review it.

To "focus" on multiple contexts, can't you just select those contexts and create a perspective displaying them? If you group by context, it's even easier, because you have, say, "Office" tasks as well as "Waiting" tasks all in one view, but with the Waiters below Office, and therefore visually de-prioritized.