Hello,

Currently, the support for this is only by using a workaround that would be a definition of smallest sold amount, handled later as one item / a unit.
Then you could modify the default transformations and controls for adding products so that the customer would add values in meters and the code would calculate amount of units - items needed. Also some logic would have to be changed in shopping cart listing and invoice template. This will likely require to use custom E-commerce providers, however it's quite easier since 5.5R2 version, because it's possible to add them to App_Code.

Would this principle be feasible for you?
Should you need any additional details, feel free to ask.

Regards,
Zdenek