I have an Idea!!!!
Simply remove the extention of the file....
Than go to WinRar, go to the folder of the file, select it and click on "Add".. It'll open the RAR options and than selct it to Split.... You can change the Coprension Metohd too...
PS: When decompressed, you will need to put the ".rar" back to decompress the "original" file... but....