What I did was to install iDesk, it works pretty well and it's "relatively" easy (it's a bit tricky to place the icons correctly as you have to estimate where it will be).
I guess if you type iDesk on any Ubuntu forum (and even on the Mint one) you'll find the information you need quite easily.
 I think it is installed by default so to find out, go to the Home folder, press ctrl+H (to view the hidden files) and if you have a folder named .idesktop then it is installed. Normally you'll have the file .lnk for the desktop icon so what you need is to use that as a template.
For my Firefox icon, I have the following command:
Then you save it under firefox.lnk and you'll have a firefox icon next time you restart fluxbox.
Width and Height refers to the size of the icon
X and Y to the position of the icon on the desktop (the starting point being the top right corner)
It's pretty basic, but I'm not an expert, I've only started using FluxBox last week so it's all new to me
Anyway, I hope it'll help