Incremental dats are not supported by the command line scanner, you will not make that work.
All you really need to do is:
1. Host the daily avvxxxxdat.zip archive somewhere (where xxxx is the dat version).
2. Copy the zip file to the client.
3. Unzip the contents of the zip to the uvscan install directory, replacing the previous files
4. Run uvscan --decompress to pre-initialise the dats and thus improve overall scan performance. (Not essential, scans will still work without this).
2 & 3 are interchangeable - so you can unzip the files first then copy them over too if you prefer.
Just make sure you do a binary file copy
See McAfee support article KB6713 for a little more detail on options, such as where to find the tar files for example. (these are not hosted via ePO but are separately posted to McAfee ftp)
Finally, please note that McAfee cannot support customer-generated update scripts for uvscan.