Not possible. However, once uploaded it would be easy for the user to add the images as attachments to the steps.
If you exclude the Excell Add-in you could build your own API script that could create the tests in QC AND add the images.
If you go to the QC API help files and have a poke around you will fidn what you need. Otherwise just search these forums, I'm sure someone has already provided a full script to do what you need.
While I have been working for Businesses that are Vendor partners with HP, IBM and Microsoft, my opinions and advice is my own.
The solutions provided are either sourced from my own scripting libraries or from a quick Google Search.