Way to choose subset of keyboard layouts

Binary package hint: gnome-applets

As a user of 3 layouts (English, Hebrew, Russian), I find layout switching unconvenient and error prone.
I need to press the layout switching key sometimes once and sometimes twice to toggle between two layouts.
This requires a lot of mental state, so I frequently make errors and start typing in the wrong layout.

What happens in practice is that I only need 2 layouts at a time:
 - At a given time, I work in one language context - English, Hebrew or Russian.
 - But English is always needed (command line, URLs, keyboard shortcuts).

So removing the layout I don't need at the moment improves the switching experience a lot -
with just 2 layouts (+ keyboard LED feedback), layout switching becomes trivial.
But the existing interface makes removing and then adding back layouts too cumbersome to be practical.
What I would really love is a way to disable layouts temporarily.
(I ended up writing shell scripts to do "setxkbmap en,us", "setxkbmap en,ru" etc.
But I believe a GUI solution would benefit a lot of people in similar position.)

I can imagine 2 interfaces:
 - Checkboxes in layout menu to disable/enable individual layouts.
   Ideally, clicking the checkboxes should leave the menu open.
   When the checkbox is disabled, the layout name should be grayed out, and skipped on keyboard switching.
 - Hardcoded model of 2 languages:
   One layout would be the primary layout, always enabled.
   Choosing one of the other layouts by mouse would automatically make it the secondary layout.
   Keyboard switching always works between primary and secondary.
The second approach has the potential to be more effecient in use (by how much? one click?)
but is harder to understand, less discoverable and requires configuration to enable and choose primary layout.
(Can't assume primary layout is english
The first approach is visually obvious, trivially includes the case where all layouts are active.

In both cases (and in fact unrelated to this feature), switching by right-click would be easier if the layouts were moved from a submenu to the top level of the keyboard indicator menu.

I'm not sure if switching by left-clicking the icon should include all layouts or only the enabled ones.
I'm inclined to include all, because if a person placed the mouse on the indicator, he is already looking at it and the visual feedback should make repeated clicks easy.

P.S. on the discoverability front, the indicator tooltip should also say which key(s) switch keyboard layout.