I am not aware of such an option for stock ICS. USB and adb are required for all of the methods that I have seen for ICS on the Iconia.
I am not sure that I follow your reasoning though for how you believe that rooting would help. I have a few a500s and an a100, and all are still as fast as they ever were. If your tablet is running slower than in the past, you may need to clean house a bit. If it's merely browsing that is slow, then maybe some changes to browser settings, or use of different browsers may help. There are a number of things that can affect browsing performance, including:
* change in web sites, pages
* the bowser being used
* the browser settings (one improvement is to use flash only on demand, not automatically)
* the number of browser tabs open at any given time
* network performance as affected by: distance from the wifi source, wifi or Bluetooth interference, router issues, ISP issues, etc.
* running with both wifi and Bluetooth radios on
* the Acer Iconia ICS sensor bug, which causes error messages to stream into the system log at a rate of 20 per second (not all tablets are affected, but many are)
* the Acer Iconia ICS GPS receiver diagnostic log leak that accumulates files under /data/gps and invisibly wastes storage space
* having too many apps installed, especially where certain apps use excess CPU while running in the background
* having too much data in your /sdcard folder (avoid using more than 75% of the total available space, or the filesystem becomes less efficient)
* problems such as errors and fragmentation in the /sdcard filesystem (a factory data reset will clear this by recreating the filesystem as new)
The last four items listed above seem to occur inevitably over time, and a factory data reset can mitigate the effects significantly by restoring the device to a fresh new state.