I don't know about Windows, but I have been having this issue with Mac OSX and wrote a simple applescript to access the printer webpage every 50 minutes to reset the sleep clock. Its annoying to have to do it this way but beats having to powercycle the printer all day.
on run {input, parameters}
repeat
tell application "Safari" to activate
tell application "Safari" to open location "(printer webpage)"
tell application "Safari" to delay 2
tell application "System Events" to key down command
tell application "System Events" to keystroke "w"
tell application "System Events" to key up command
delay 3000
end repeat
return input
end run