I've asked the question on the IRC, whether I'll get a response tonight is another question but as soon as I get an answer I'll edit this post to mention what the response was.
I imagined it was pretty much making the same IP's route down two or more lines via clueless and then a bit of work for me to do on the router to support this fully. Maybe I'm wrong but we'll see, hopefully I'm not.
EDIT: Someone has confirmed on IRC that while they obviously charge for the additional service (e.g. VDSL2, line rental or whatever else that usually applies), they don't charge for bonding on top.
Edited by Ixel (Sat 17-Mar-18 20:40:32)