There is no obvious mechanic but one that make sense to me is:
If there are more width dice than the character needs to succeed then they can be transferred to increase the height, say, at a two to one ratio.
So if for example you got 10x10 and you only need a width of 4 then you can change this to a 4x13. Results above 10 are virtually impossible feats.
It might be best if they players does not know what the required widths are, then you can get results like, "you tried too hard to get that /arrow in an arrow shaft shot/ and the bow snapped".
Also for remarkable failures as the number of dice increase it become unlikely for any fail, so may be you should use the width again. If the width of the roll is two (say) less than the required width, then it is a fumble and the height, or rather the lack of it, gives you the level of fumble. Hence say a player get 6x3 and decides to shift this to 2x5 thinking that is is a better result, but unknown to them a width of 4 was required, then, this is a level 3 fumble.
Hope that helps.