Migration Virtuemart 2 to 3 stockable plugin shoe size problem

[badslayer]

We are working on upgrading Joomla 2.5 to 3, and Virtuemart 2 to 3.
However I understand that the stockable custom fields do not work in Virtuemart 3.
http://docs.virtuemart.net/tutorials/installation-migration-upgrade/198-upgrade-virtuemart-2-to-virtuemart-3.html
http://forum.virtuemart.net/index.php?topic=127867.0

Our problem is that our store is a shoe store which uses the stockable plugin with 'Size'.
Each shoe has different sizes with different stock.
For the stock we use Advanced inventory for Virtuemart the stock seems ok.

If I understand correctly the procedure is to "Remove old vm2 inherited customfields" to fix the fatal errors concerning stockable(VM2) plugin.
However removing would break all the current 'Size filter' between the products and we don't want to rebuild the products or remake the parent / child structure.
How can we solve this issue without re-entering the products and sizes?

[jenkinhill]

Instead of having a stockable plugin there are child variants now which include stock control. But not yet a tool to update stockables from the old plugin. See http://forum.virtuemart.net/index.php?topic=125866.msg440724#msg440724

[badslayer]

any idea when it's available?