Breastfeeding a toddler and donating plasma?

I have a 1.5 year old who nurses once during the day. I really want to donate plasma, but you aren't allowed to be bfeeding at all. I really don't want to make him give up the last feeding yet either. I just don't see why they won't let you donate if you are breastfeeding, and wonder if it would be ok to lie? I mean at 1.5 years, he just does it for comfort, and I doubt I am losing that much as far as antibodies/protein goes with one small feeding a day. Is it really a big deal, or are they just being ridiculous?