That's pretty much the way I found it: you have to dig down to the file section in iUploader, then look around for the upload button. When I uploaded, it looks like it stalls and iUploader crashed a couple of times, but the file was there and intact when I went back to find it.
Internet access wasn't required. I was using the 505 as a standalone device, without an Internet connection.
To upload via a browser (like the one in iUploader) you need a way to transfer a file from the sandbox of the program used to create it to the browser's sandbox. The iPad's "Open In" function is the only way I know of to do it directly, without an Internet connection. I don't have iCab, but none of my other browsers support that.
I was using http://192.168.0.1:8181 to access the Shareport web interface. I just plugged the 505 into a wall socket (no Ethernet or WiFi connection to the Internet). Then I connected to the 505's WiFi SSID, launched iUploader, entered the above address in the browser and it worked from there.
iUploader was glitchy, but it worked and that's fine by me.