So in rules like Pike mens lament and For the men who would be kings where units are of say 12 figures do you just play with bases of multiple figures to represent one figure if using 6mm?   Thats the only way I think it can work in my mind at least.  Who has done this?

I have the Men Who Would be Kings and I plan to use the 3,2,1 basing method (see my post in Painting & Modelling, there is a link in my last post).  Ahead of receiving my order I've done a few tests with counters etc. and the only downside is the number of bases you need to move but as a solo player this doesn’t bother me.  I’ve not yet worked out the actual bases sizes I’ll use as I’ll do that once I have the figures e.g. what looks good & would several 3,2,1 bases equate to 1 big one etc.

1 base of 12 (12) or 6 bases (1,1,2,2,3,3) 

3,2,1 as Ted would say, would allow a unit to be as big or small as you wanted 

You could certainly create bases with one or more strips of 6mm, then treat these as "figures" as per the rules.

It may not produce the appearance you seek, the rules emphasize spreading the bases out (unless in close order). So you won't betvthe impression of a neatly dressed batallia.

I initially played TFL's Dux Brittaniarum in 10mm with three figures on a 28mm figure's circular base. It worked well and actually looked like an army.