Bonding with EdgeRouter-4

I was wondering if anyone could provide any pointers or direction on getting line bonding (2 x VDSL, through AAISP) working on an EdgeRouter-4. I understand that the download is handled their side, but would like to benefit from bonding the upload, which I need to configure my side.

I've seen a few posts of people saying they've got it working with AAISP and an ER-4, but not giving any more details (and the posts are often a few years old, so I doubt their accounts are still active).