@Stomm, putting the various reasons why it likely won't work aside, what 'shape' brigades do you normally field?
I field 120mm wide x 80mm deep infantry brigades generally. I sometimes also field 240x40 brigades, but usually a kind appears mid-way, when facing another army with cannons this is my favoured infantry formation as it minimises bounce damage.
Cavalry, well I usually start them off as a large blob, but then send them off into brigades of two, three and four in all sorts of formation. So movement trays really are of little use to cavalry as they hardly ever adopt a straight line or block formation after turn one.
As an aside, Og Games sell both magnetic sheeting and metalised sheeting. If you wanted a super-quick movement tray solution, cut the metalised sheeting down to size without taking the backing off, apply magnetic sheeting to your bases and there you have an instant flexible movement tray. Stick to plasticard for more rigidity if you so wish.
A much better solution is to flock your boards with iron filings, magnetise your bases and there you go, the ski slope problem solved...