You can get some free editor with syntax highlighting and use it as external editor for WinSCP, cannot you?
A module/plugin which color codes all or certain lines and types of code would be fabulous. Because i edit my PHP scripts live over FTP i don't use a separate code editor and this small extra that comes with some of them i've never seen in an FTP program.
Even if the code highlighter just hightlighted the comments, which could be user definable (comment syntax being language dependant) this would be absolutely awesome...
Great job with WinSCP