As a Grunfeld player my first instinct is 1. d4 Nf2 2. Nd2 d5. But this might get me in trouble if say 2. c4 g6 3. cxd5 Nxd5 4. e4 because I can't play Nxc3. So probably 2. c4 c6 and now we 're both unhappy because I'm playing something that is not my opening (is this roughly the slav?) and you're playing something where your knight is probably misplaced on d2.
I don't know why you are trying to transpose into the Colle. Is there anything keeping you from getting the Colle setup with the usual move order?
What do you all think of 1. d4 Nf6 2. Nd2!? If Black responds with d5, White can transpose into the Colle. After c5, White can play dxc5 and force Black to somewhat waste time to regain the pawn back. Sometimes this transposes into the Tarrasch French or a line of the Pirc. Is there anything that you would play against this?