I have a T-P type roller blind shutter.Yup, they're old. but its' the one shutter I've got for a bunch of brass lenses I'm experimenting with.

It has a large hole, and is quite big, front mounting. I'd like to use it for a smaller lens than was on the camera it came with.
does anyone have a DIY way to make some sort of gasket for the inside of the hole? To make it sit properly and not have it fall off. I've tried a variety of ways, but short of taping it to the lens and lining the inside of the hole with something to make it smaller, I'm not coming up with any ideas.

Thanks