Mapping IC based if account is IC

We want to set the IC value to none if an account is not IC.  We are currently doing this in the IC dimension in the datasource and looking up the account, getting the target and then checking If IC.  If it is not IC we pass None as the source value.  This works fine unless they upload a new account because it has not been mapped yet it doesnt know its IC and maps to None.  The user has to reupload the same file after they map the account so that they get an IC value in the source.   

I was thinking that I could put a BR on the IC transformation rule but the problem is it reads the 1:1 (where I have the None->None) before it gets to the section for BRs.   I guess I could remove the 1:1 None rule and then in the BR check to see if the account is IC and if so then get the IC target.   

I am just curious if there is a better way to handle this that I have not thought of.

We have a similar issue as we store function in a user field but we only want it populated for specific expense accounts otherwise it should be none.  When they have a new expense account we have the same problem that they have to reload the import file after they map the expense account.