maybe you can just put the filter in front of the lens
yes that is the idea.
But the question is how to do mechanical smart?
I find to do with a piece of tape is a little bit botching (and unsafe for the filter).
I already playing around with an old remounted front tube of an eyepiece,
since these has a inner filter thread on one end and a (now abundant) inner eyepiece thread on the other.
Last I can cut shorter and mill away some millimeters so it matsch tight over the lens outer front edge.
(And secure it with a little clamp).
Since no one here has a better Idea, it seems like I have to give it a try that way.
And hope the best