How about this?
Instructions:
1. First sentence
2. Second sentence
`This is some code.`
3. Third sentence
4. Fourth sentence
It wouldn't indent each point, however your example with the dots doesn't do it either.
If the spacing between Instructions:
and the rest is not what you want, you can use the double space after it and on the two following lines.
UPDATE: After a little fiddling, if you want to keep the numbering of the list and put some code that's relative to a single item on the list you should indent the code block. Also, have a new line before the first element of the list seems to help.