Of the numerous strategies that have been proposed for stemming the foreclosure tide, many involving Federal Housing Administration refinancings, few if any start with the investors holding troubled mortgages.That is where National Bank Of Kansas City has been looking for opportunities to boost FHA volume. Since January the $963 million-asset Overland Park, Kan., unit of Ameri-National Corp. has been approaching noteholders with a proposition: Identify loans in your portfolio that you would like to unload, and the bank will solicit the borrowers to refinance.