How to place SuperFetch cache on an SSD?

Disable ReadyBoost. Make your SSD your primary / boot drive, and / or make sure your pagefile is on it. ReadyBoost is just a secondary buffer for stuff - if your pagefile is fast enough you don't need to use ReadyBoost.

Even if you can't make the SSD your boot drive, you can still tell Windows to use the SSD for your page file. Either way it eliminates the need for ReadyBoost.

Turns out you cannot put a ReadyBoost cache on an SSD.

When you initially format the drive, and assign it a drive letter, you are given the option to place a ReadyBoost cache on the drive.

But on subsequent reboot, the ReadyBoost driver reports in the event log:

The device (Unknown Unknown) will not be used for a ReadyBoost cache because the ReadyBoost driver is attached to its volume stack.

Full log entry:

Log Name:      Microsoft-Windows-ReadyBoost/Operational
Source:        Microsoft-Windows-ReadyBoost
Date:          3/2/2011 10:55:28 ᴩᴍ
Event ID:      1022
Task Category: ReadyBoost
Level:         Information
Keywords:      (16384)
User:          SYSTEM
Computer:      Harpax
Description:   The device (Unknown Unknown) will not be used for a ReadyBoost cache because the ReadyBoost driver is attached to its volume stack.

Even though a ReadyBoost would be useful for a computer running on spinning platters, ReadyBoost seems to limit itself to storage devices connected to the slow USB port.

Look at motherboards that support Intel's Rapid Storage technology. It allows the use of a SSD as a cache for your magnetic/spindle hard drive.