i assume you're looking to make spark in the chamber? best idea i know of is to send two screws into the chamber from the outside, then you can adjust the distance between the tips of the screw for optimal spark. then solder the wires to the head of the screws once you've got the distance about right.
i've HEARD that works pretty well.
an ignitor from a grill works good. either that or from a gas log firplace. i prefer the pnuematic type myself, none of those issues to deal with. and how will you get the plug into the chamber??? just screwing it in could mean a flying spark plug. just a thought.
finally something I can add to the site! I have used a grill ignitor with good success. they're probably not the most reliable but cheap and replaceable. drill a hole directly in the meaty part of your cleanout cap and epoxy in place. many potatoes have left the dangerous end while the ignitor has never left the friendly end.
My old one used a coleman lantern sparker... a little twist/ flint jammy. Lost the whole assembly and wanted to try to rig one with an electronic trigger. And curious as to the responses this would get.