I have a tip - I don't use masking tape, but I do use low tack frisket for masking off designs for airbrushing. To ensure that it's even lower tack, I stick it to my t-shirt, or jeans, or whatever before I use it. It usually stays tacky enough to mask the area, and picks up enough fluff from my clothes to form a barrier between the adhesive and the leather which means it's less likely to lift the surface.
Masking tape is far more adhesive than frisket, so I'm not sure it would still work, but it's worth a try on a piece of scrap?