Simple one level permalinks for my pages

Hello WP community,

i have a little issue and cannot find proper answers in the net. there is a lot written about the category base issue, but there was no solution yet that fits to my need and i now hope the specialists here know immediately what i want and how to get there.

what i want is simply to have wordpress naming my permalinks of all my pages one-level, meaning:

if i have a menustructure of lets say m1-m2-m3 with each having submenus m1a-m1b m2a-m2b etc, then with the permalinks set to %postname%, still WP will add the parentmenu to the permalink: domain.dom/m1/m1a

BUT i want to have JUST the pagename single, for all pages in all depth, domain.dom/m1a, domain.dom/m1b, domain.dom/m2a2b5whateverdepth, etc.

so how can i get WP to stop automatically adding the parentmenu? It offers me to choose pure %postname%, but then still adds, can this behaviour be stopped? there are solutions for manually editing the permalinks for each page, that would work but i search for a way to stop WP adding it, not manually removing after. a tiny plugin, or a core hack if it must be.

Any up-to-date solutions to this not so young issue?
Thank you to all
Sofian