Do your research before you pull this one. If it turns out that her parents are spending their golden years in indescribable bliss, then this will definitely work against your purposes. Luckily for you, this is almost definitely not the case. We put the chances that your girl's parents are still in love at roughly 5 percent. Odds are that you'll spend the weekend trapped in the guest bedroom using Spotify as a bulwark against the incessent bickering going on in the living room. The mutual nagging of the aging parentals should drown out any wedding bells that have been ringing in your girl's ears.
We can't impart upon you enough how judiciously this method should be approached. There is a significant chance that a) the trauma you endure from the experience simply won't be worth it, or b) her parents will love you, thus adding two big-time cheerleaders to the opposing cause. On the upside, it's probably been a while since you've had a solid homecooked suburban meal, so that should be nice.