I have tried all your methods, but they didn't work for me, in fact I have created an easier method using MS Word Tables.
Pros:
Cons: It will not maintain code colouring although someone could improve my trick.
Steps:
Insert a 3x3 table, in my case I always make the total width of the table equals the free page's width (3 rows minimum to test the tables style).
Use invisible borders ("No Borders" option), and activate "View Gridlines" option. it should have this aspect. Be ware that those lines are for you to see the table's grid, and the will not be printed.
Make the adjustments to cells' spacing and columns' width to get the aspect you like. (You will have to get in "Table Properties" for fine tuning).
Create a "Paragraph Style" with the name of "Code" just for your code snippets (check https://stackoverflow.com/a/25092977/8533804 to get the idea, you don't have to follow all of it)
Create another "Paragraph Style" with the name of "Code_numberline" that will be based upon the previous created style.
In the newly created "Code_numberline" add the numbering style that you like (this will automate line numbering).
Apply "Code_numberline" to the first column, and "Code" to the 3 column.
Save that table style and enjoy!