I will add to what Katrina said and say that the toddler years are SO much easier with that connection to fall back on, but to answer your question...
Start with the nursing session he is least interested in and as others said cut one out at a time "gently, with love." Don't necessarily do it a week apart (what has gone on a schedule this far?), just cut another out when he seems ready, this may be a week, it may be 3, it may be 2 days. Just follow his cues. Don't think of it as more time for you yet, as you must distract. Change this nursing time into quality time, reading, cuddling, playing, etc. I'm glad you've had such an easy time breastfeeding. I AM someone who nursed my kids until they self-weaned, and I did want to comment because of your first sentence. Though I have enjoyed the benefits of toddler nursing and love to share that with anyone who is interested, I am not ignorant and realize that not everyone wants that. I feel a bit lumped into a category and dismissed out of hand. For great weaning advice, call your local La Leche League...
K.
PS. If you get engorged, take notice. pump until you hurt no more (not more than that if you want your milk supply to go down), but don't let it go, as you don't want to end this beautiful journey with mastitis. Also, cabbage leaves really work for reducing engorgement and lowering milk supply.
pps. you can just night wean, if you'd rather. Elizabeth Pantley's book the No Cry Sleep Solution is a great book about night weaning.