When I am booking a stay for a MR purposes only, I'll usually book the cheapest rate which is prepaid. So sometime during the day when it is convenient (unfortunately early morning is best for me and the particular hotel I use for MR is not great about checking someone in early, even if the room is available), I pass by the hotel (usually a little out of they way!), check in, get my key, and usually go up to the room to at least make the towel look used and pull back the bedding. Just feels too wierd to at least not 'enter' the room, which I'm sure in this day of electronic key cards they can tell everytime someone has entered the room. Anyway my stays usually last 10 minutes, so at least I don't have to pay for parking as well (under 30 minutes no charge for parking, otherwise 18.). Not all SPG properties have parking charges of course but in my area, not so uncommon.
But if you are really worried about stay credit, then check in, even for just a few minutes. If this weren't required, many of us would be booking the 50. rate in one of the cheaper hotels that might be hundreds or thousands of miles away!