I need to lose some kg before my surgery.... in a month

I'm not extremely overweight - I'm 80 kg at 173 cm, which is a BMI of 26.7, which is not a healthy weight but not too bad I don't think. However, the nurse explaining my upcoming surgery to me did mention that losing a bit of weight would reduce the risk of complications. I do exercise a reasonable amount, not a huge amount, and I can't really increase my exercise because of the health problems leading to my surgery, but I do struggle with binge eating which is making it hard to lose anything.

I'm think of doing a fairly heavy regimen of meal replacements over the next month. So, what is a reasonable amount I can expect to lose in 5 weeks if I used meal replacements? Ideally, I'd want to lose maybe 6 kg, to get down to the top end of a healthy BMI. Is using meal replacements a good way to drop some body fat fast? Is it safe? I know its not a sustainable long term solution, but I'll keep working on my binge eating and increase my exercise after I'm done with the surgery.

Thanks everyone!