VM 3 - Dropshipping management / sum of two or more shipment methods

[vittoriobruno]

Hi all,
I am currently working with Joomla 3.4.4 and VM 3.0.10.
Our shop has to deal with dropshipping and several suppliers want to send their own courier for the shipment.
Let's say we have supplier A and supplier B: each one manages different weight ranges with different costs. I set two different shipment methods, one linked to supplier A and the other linked to supplier B (using dummy categories for instance). Then, when any user orders one product of supplier A and another from supplier B, VM allows him/her to choose the shipment method at frontend. Is there any way to ask VM to sum two (or more) shipments?
I tried setting a multivendor shop but it doesn't work anyway. I don't understand whether the blocking categories in shipment configuration could be used someway. Maybe some extension/plugin is needed for this purpose.

Thanks!!

Vittorio