There are two links in the FAQs on scout mounts, one with links to previous discussions on them, what you're thinking of is sort of a modified scout mount, there are a couple pics of that in one of those links also. Someone recently did something similar using an extended ring on the front of a standard length base, the other option is to buy, beg, borrow or steal one of the discontinued Ultra rails which is an inch longer than a standard base.
Tim