Big pants suggests that best guess at V1 and flex temp might be good.
Problem with that idea is that there's so many variables on V1 other than weight, such as wet versus dry. I'd suggest VR/V2 for a given weight and flap setting would be a better indication to compare to your flex.
We've recently switched to Airbus fly smart iPad software, it's a great bit of kit but I've certainly started doing a lot more gross error checking of speeds flap setting and weights prior to departure.
Our outfit recently had a flap 2 takeoff on a runway which should have been set to flap 1, luckily this was a 'conservative failure', had it been the other way around there would have been much gnashing of teeth. As a result of this we found out that the flap indication in the MCDU provides noTO CONFIG warning in the event that it does not match the selected flap. My point being, it's not only the weight being correct that is critical.