By overriding the accounts, I assume you are referring to accounts that are translated historically as opposed to the default translation performed by HFM?
If so, I have seen two general approaches to achieve this:
a) Allowing the user to directly override the translation at IsTransCurr (i.e. <parent currency> if parent is in a currency other then entity)
b) Entering in a special currency rate in a rate account and then adjusting the translate routine to translate your account by that rate.
I personally, am a bigger fan of the first option.