Marketpress network-wide categories hierarchy

I'm building a project that has the following:
1. A "template" blog. Every blog users create is a clone of this one.
2. This "template" blog has MANY (800+) product categories which are of course cloned to all other sites.
3. The product categories terms are organized hierarchically.
4. Any updates to the template-blog's product categories are synced to all other sites on my network.

So far so good...
When users create a new product on their site, they choose a category (using this plugin has made it really easy to choose and navigate all those terms).
Here comes the "but" part....
On the "global" store I have to display all product categories so that users can navigate and choose what they want to see BUT global product hierarchies are non-hierarchical. As you can imagine, having a list of that many categories sorted alphabetically with no structure at all is not functional and makes no sense.

So my question-request is this: How to display network-wide product categories hierarchically??? I'm sure I'm not the only one who would benefit from something like this!