Would not recommend completely dry fucking. I have taken average to large with no lube other than spit. Sometimes it happened, other times it didn't. The times I was successful, they only happened after being rimmed thoroughly, and he had a nice layer of throat slime on his cock. Then it was really slow progress, and it burned a tad.
You have to be exceedingly careful in doing this. While I doubt you would need a colonoscopy bag, you could tear, and anal fissures are not fun.