Thanks Tonyr,I don't think Pan's approach will work in this case. Looks to me like you're going to need the correct pot.
One thing that mod doesn't have is temperature feedback. In other words, setting the temperature depends on your ability to test the temperature at the tip independently. Perhaps a rotary switch with a number of resistors to give you the desired temperatures. That way you'll have a ballpark temperature in mind.
A four position rotary switch should give you enough choices, although a pot will give you infinite temperature choices over its total range. I'd opt for 480˚• 440˚ • 345˚ • 200˚ (Celsius). Being in the U.S. and more familiar with Fahrenheit; those temps covert to 896˚ • 824˚ • 620˚ • 392˚ (Fahrenheit).
"four-position rotary switch" seems to be doable with predictable outcomes
If can not catch hold of any pot conversion methods, I will definitely take this route.