Custom command to create split/multiple tar arhives

Hi!
I recently started using WinSCP and I must say I LOVE IT. The custom command section is awesome. There is only one custom command I'm missing.

I want to be able to pick a file or folder and tar that one into several smaller files, say 100MB each. And that they would be extractable on my windows vista box afterwards.
file.bmp ----> file.part1.tar.gz, file.part2.tar.ghz, file.part3.tar.ghz

The reason for wanting this is that I want to make sure that I dont have to download the whole file again if it turns out to be corrupt when I finnish downloading it from my ftp.

Is this even possible to achieve?

You can setup such custom command as long as tag and/or gzip allows splitting target file (I'm not an*nix expert). But you cannot make custom command download the files automatically.