OK, dontcry, if you say so. But at the risk of sounding prescriptivistic, this seems to me more like a misspelling (or a "creative spelling" as one of my teachers used to say) than a variant of "temptatious."
Rolig, I called it a variant rather than a misspelling because it gets more than 10% of the g-hits relative to temptatious. But on Google Books, there's only one bona fide usage (after excluding OCR errors), which means editors don't let it stand, so I agree that it's a misspelling. I added it to my panvocalic list after dontcry commented on it, but have dropped it now.
I just realized what your reasoning was, dc: temptation + capacious. Got it.
Mollusque, as you know, there are a lot of crazy spellings out in Googleland, especially on web pages written by people who do not have a firm grasp of English (I mean that English is a second or third language for them). I respect your checking the word on Google Books. I will have to remember that.