I was asked recently on bitsharestalk how to make a direct URL link to select the input/output coin pair (in fact, IIRC, it was what that URL would look like to buy STEEM with BTC) that would be suitable for embedding into a web page, for example. The basic template is:
https://blocktrades.us/unregistered_trade/input_coin_type/output_coin_type
So for BTC to STEEM, it would be:
Yes, this is what I asked to you! Great!
Yes, it was your question on bitsharestalk that inspired this comment, but I accidentally never pressed the post button to reply to you there (too many browsers windows open, I guess).