With CodeWright (and probably other decent editors), you can select a block of text & then choose a button which will automatically put the comment-introducer (whatever that may be for your particular language) on the front of every line of the selection.

Even if your editor doesn't have this built-in, it wouldn't be hard to record a suitable macro.

Or maybe you could use the search-and-replace facility to replace all the "end-of-line" marks in the required range with EOL;

If your editor doesn't support any of the above, throw it away and get a proper editor!