Dude, no matter what… USE LUBE! The micre-tears it can create internally can become an issue in the future... INSIST on it.
If not, there are some lube caps, you put them inside your anus, and they will melt and lubricate your insides. You put 1 or 2 inside 20-40mins before going at it and he won't even notice it's lube. 😉
Here are some:
hxxp://www.lubrin.nl/contents/en-uk/d4.html
hxxp://www.shytobuy.co.uk/lube-in.html
hxxp://www.condomsaustralia.com.au/wet-stuff-silicone-bodyglide-lubricants-capsules-p-1850.html
I'm sure you'll get the idea... the rest is up to you.