This is without a doubt the easiest and sneaky way to propose, and to sort of know the answer before actually doing so. All the materials you need are
1. A cheap piece of funny jewelry. I.e. a rhinestone bunny face pin.
2. A fancy jewelry box.
3. A real nice diamond ring.
4. Flowers
This is what i did, I didn't do it actually to be sneaky or to fond out beforehand but just for a few laughs. In my case she picked out the ring and stuff beforehand so it really wasn't much of a surprise when I gave her the ring. Basically you meet up with her give her flowers, take her to a nice dinner and then after the meal over some coffe pull out the bunny pin in the fancy box and hand it to her. She will automatically assume it is an engagement ring and that you are going to ask for her hand in marriage. At this point you will know the answer. If she gets excited and rips the damn thing open and then gets royally pissed, the answer is yes. However, if she acts uneasy and hesitates and then is relieved to find the bunny pin then you know the answer is no. Either way you didn't actually ask her to marry you. At this point if the answer was "yes". You pull out the nice big diamond and give that to her, not only will she be happy, but she will get a laugh out of your little joke and remember that damn pin forever. On the flip side if you deduce the answer was no. You do not pull out the real ring and just have a few laughs over the prospects of marriage. (saving your skin)
Just a few thoughts...