Period Sex?! HELP, ASAP!

Tomorrow I'm hooking up with my FWB for the 1st time but I just started my period tonight! :( he said it's fine but he wants to have anal...any tips on how to make it not...painful? (Again 1st time with anal). Do you think if my periods not too bad it won't make a mess and I'll have more options??? I want us both to be able to climax and I really need clit stimulation to do that. Please help!!!! Thanks!