Stacked primary: how to?

Some time ago there were some posts about winding a primary composed by two
stacked pancakes. The idea was to set the inductance by setting the spacing
between the two stacked coils (no tap anymore required).

Considering that the primary will be made of copper pipe, has anybody got a
mechanical solution about:

- how the spacing between the pancakes can be changed
- how the pancakes are connected to each other (a flexible joint or what?)

Has anybody at all tried this solution?