No stake in this, just a suggestion and also a little curious. Could a shortcut pinned to the tab or nav bar work? I keep my email in a pinned Safari tab.

I second whynaut's suggestion.

That's precisely what I did for the elders.

I set up pinned bookmark shortcuts on the 'tab bar' (had to enable the 'show bookmarks bar' option).

Now they have a button for 'mail', one for 'search', one for 'maps', and one for 'facebook' etc. Those buttons are always visible, no matter how far they venture into the internet. Solved the problem for them (or rather, for me, lol)

I imagine you can inject the necessary buttons via userscripts, if this is truly a “hard requirement.” The bookmark bar is, of course, the standard solution to this.