Allow user macros in items custom multiplier

It would be cool to be able to use host macros in item's custom multiplier. For example i would like to generate graph which is showing read/write bytes from/to HDDs per second. This is unfortunately not supported in linux so i need to use 'sectors per second' (btw, shouldn't this be called 'blocks per second' ?) - in this case i need to multiply it with block size which is saved as macro in host.