How to pass additional context info to Converter

Currently Converter methods receive both model and presentation types and locale as parameters. But what if the Converter needs to perform value conversion additionaly to type conversion? Example - we store in the database worldwide temperatures, in US the values are in Fahrenheit, in Europe in Celsius. The end user expects to see the normalized data only in one unit, probably depending on Locale. Similar conversions are needed for othe technological units like length, area, etc. In our environment we store the additional info (units, status, …) as Context along with value in the Property. Unfortunatelly the Converter has no access to the Property. Any idea how to solve such type of conversion. Please do not advice to normalize the units on database commit (ex. save all teperatures in Kelvin), it’s old application and I cannot change the data model.