How to whip Emacs into weird indentation rules with tabs+spaces?

[Juanma]

Hi ... again.

The question is, for C++ code, how to make Emacs insert tabs for "main
indentation" and spaces for "sub-indentation". Example:

|---| = tab     . = space

|---|while ( something &&
|---|........some_else )
|---|---|then_do_something();

The idea is that tab goes one level further, but for same-level adjustments
only spaces should be used.

How to force Emacs into that insanity? (no, it's not my personal choice)

Many thanks.
-- 
Juanma

"Having a smoking section in a restaurant is like
 having a peeing section in a swimming pool."
       -- Edward Burr