My dd self weaned at about 14 months and when she was 16 months my ds was born. My dd has always asked to nurse since ds was born. I actally just let her, and she wanted nothing to do with actually nursing I think it was more the cuddling and me holding her she missed. But every now and again she'll say "Mommy, I hungry, I eat boobs too?" and I'll invite her up (with my shirt fully covering me)- and she'll just rest her head on me and snuggle. (by the way she'll be 2 at the end of Sept.) Every time though I remind her all of the awesome things big kids get to do.. drink juice, eat pez (her fav. candy) play outside etc..
Honestly, if it were *me* I'd just let him sit with you like you would nurse, but be fully covered. 1 so he doesn't feel replaced and 2 maybe he just wants to snuggle. But also remind him what a big boy he is.