Don't worry - i'm convinced that you'll be able to pull it off without him noticing at all

Sea sponges are good to use and absorb really well and you can find them anywhere, boots, tesco's, bodycare etc. If you can't find a sea sponge then a regular bath sponge works just as well, you could even use a car sponge lol providing it's brand new and unused ofc.
Cut the sponge in to smaller parts and fold one of the parts in half, wet the sponge segment slightly and lubricate yourself, insert the sponge inside pushing it as far back as it will go. Don't worry it won't get lost

I've needed a quick fix on a couple of occasions and it's never failed for me. I've never had a client notice as far as i'm aware and nobody has ever mentioned me being on my period when i were

Good luck!
PS, probably best not to allow fingering like mentioned. I use the excuse that i've just had a coil fitted so find fingering uncomfortable at the moment, they don't tend to press the matter x