Sadly, there is nothing you can actively do to properly help him out.
What he should do is find a group whom he'd be able to share exp and then he could properly get exp.
Regardless of what you block his damage output will not suffice to get him a proper exp/h rate, he needs others do deal damage as well.
The whole idea of the group is not only that one can tank and another heal, it's the collective damage that gets a high exp.
I'm a MS 359, my brother a 332 ED, a friend a 378 EK and another friend a 384 RP.
The dmg is EK first, then MS, RP and ED followed kinda around the same, but the EK has the most.
My point is, you can help him in so many places and waste a lot of money with it but it's not really worth either of your time.
My best guess is that you guys (only the two of you) can pull off around 3~4 EXP/h max where as in a group he'd e able to pull over 7kk. If he's the lowest level of the group then could get even more. (other 3 level 406< but)
What you could also do, sadly involves somewhat of a charity kind of thing.
He alone can't pull the dmg output to get a nice exp, but if you call a 400MS and a 400RP and block for the 3 of them, you'd be able to hunt falcon paladins with a waste (your friend won't be able to hold you with a box of falcons, you'd have to pot a lot).
You could also do ferumbras ascendant, guzzlemaw valley, prision -3 middle rooms (rp needed to double box it), maybe carnivores -3 with rp luring it all...
To sumrise, there's not much you alone can do to help him but those are the options I see you may have.