I havn't done this in some time, so I may be a bit rusty but the Directory table in MSI does not support using a property in the column that accepts folder names. So in order to create this kind of directory I believe that you will need to use a 'Set Directory' type custom action which will allow you to create a new directory identifier based on the composite of the directory identifier representing MYdocuments\mki\ti_01\run and LogonUser.
Also, if this is internal software you may want to recommend to developent that they move to [AppDataFolder]mki\ti_01\run which is user specific by default.