No and maybe.
Let's deal with the No first:
The proxy settings need to be set on the clients otherwise they will always use default proxy settings (none) and ports.
There are two options available to you that can be used to make it easier for clients. The first is to automate the manual configuration process.
Automation. You could create a script to be run on the clients that connect to your hotspot that automatically configures their proxy settings. You would still need to transfer that script to their PCs and run it. This would be done in PowerShell / batch files for Windows clients and shell scripts for Mac OS X / *NIX clients.
Transparent Proxy. The second possibility is to use rewrite rules on the Windows "server" that is the hotspot. You will need some kind of transparent proxy for this. This is the most complex option.
Set up the Windows hotspot to also be a transparent gateway using something like WinProxy. It would then rewrite all traffic on default ports (80, 23, etc.) out 8080 on the other side. That kind of transparent proxy would be a rather complex setup though and depends entirely on how committed you are to making this work. However, in theory, it's doable. (famous last words)