Hi,
Firstly, from my discussions with a Consular officer at the US Embassy, you *dont* need to have ILR to apply using DCF. You just have to have a permanent visa in the UK (Leave to Remain is fine) and have to have lived here for "long enough". According to the consular officer, it entirely depends on your situation, and one year is about the minimum. Since you've been here over two years, even though you didnt have Leave to Remain during the first 20 months, and you've been married for 10 months now, you should be just fine for DCF. It doesn't cost anything to try (they return your payment if you dont "qualify").
Secondly, if you do have to file in the US (unlikely), you can apply while you're living here. My wife and I are both living in the UK, but we filed with the Texas Service Centre. You just have to have a US address to put down (friend or family is fine). We put down one my friends addresses in Texas, and we were just approved yesterday (applied in October)
I suggest filing *immediately* if you wanna do this as it seems that delaying one day delays the whole app by one week! I suggest filing with the US Embassy first and seeing what they say. If they accept it (and based on my discussions with the Consular Officer who denied my case, they would accept yours without any problems), it should take about 12 weeks to approval. Your first step is filing the form I-130 with them with PHOTOCOPIES of proof documents (birth certs, passports (ALL pages), marriage cert, and for good measure we included photocopies of about 60 digital pictures of us together, including ones of the wedding ceremony, plus a US-passport-sized picture for each of you).
Thanks and good luck! Let me know if you need any advice (since we only just went through this process!)
S.