On 2005-12-29, Veritas wrote:

How about one of these?

http://www.kingsolar.com/catalog/mfg/watts/4a818.html (1/2 inch)
http://www.kingsolar.com/catalog/mfg/watts/70a.html (3/4 inch)

Further googling for "tempering valve" will probably get you even
better prices.

I think a "tempering valve" may be inadequate for the task, although I
don't know the terminology very well. The specifications sheet of the
Watts 70a (the second option above) says:

WATTS HOT WATER EXTENDER TEMPERING VALVES CANNOT BE USED FOR TEMPERING
WATER TEMPERATURE AT FIXTURES. SEVERE BODILY INJURY (i.e., SCALDING
OR CHILLING) AND/OR DEATH MAY RESULT DEPENDING UPON SYSTEM WATER
PRESSURE CHANGES AND/OR SUPPLY WATER TEMPERATURE CHANGES. A.S.S.E.
STANDARD 1016 LISTED DEVICES SUCH AS WATTS MODELS L111 OR MMV SHOULD
BE USED AT FIXTURES TO PREVENT POSSIBLE INJURY. The WATTS hot water
tempering valves are designed to be installed at or near the boiler or
hot water heater. They are not designed to compensate for system
pressure and/or temperature fluctuations and should not be used where
devices tested to A.S.S.E. standard 1016 are required. These WATTS
valves should never be used to provide "anti-scald" or "anti-chill"
service.

Cheers, Wayne