You friend is not alone Wrennie in using an inordinate amount of loo roll - my youngest son uses huge amounts. Heaven knows why - he is not OCD and no he doesn't have a gut problem. I have questioned him numerous times...can you just imagine the conversations but I'm his mother so...

I have had to put it down to being 6'5" 18 stone and telling him he has a large....**se!
Now don't go checking out the size of your friends bottom

(you are not going to be able to stop yourself now are you?

)
I'm not sure about easily dissolvable toilet tissue but you can get different plys. Usually guests get the best stuff in house the really thick stuff but in this instance maybe put the cheap 2 ply there so that it is quantity instead of quality - it might go down easier. You can also get toilet wipes (like wet wipes) in packs but very very thin. A pack of those might be good.
I can't believe I just wrote all that

best of luck