make your slides and then invite them to do a comparison presentation if there is no IP issue with your current employer.
Otherwise, you may just tell them that you're concerned with IP contamintion and it's better to have a face to face discussion.
I usually have an interviewee to do an on-site first. If s/he good, I'll invite her/him to have a work experience day to do a real project. You may propose this idea to them as well.
If they're confident enough, they would accept your proposal since they would know your depth of understanding immediately as soon as you start to talk.
Good luck!
