Posting Savings Interest on Non Gregorian Dates

Background - Swabalamban Bikas Bank is planning on deploying Mifos. There is one other functionality they would like to have. I need input from others as to how this functionality should be applied.

Functionality - Saving Product Interest Capitalization SBB capitalize their interest (post) on a specific date which conincides with their bi-annual closing based on the Nepali calendar. This date can fall on different Gregorian Calendar Dates. For e.g. This fiscal Nepali year they are on Jan 17th 2007 and Jul 16th 2008. They need functionality to calculate the interest till this date and then post it to the accounts. The interest is actually calculated monthly (based on the Nepali month) on the min balance ( since mifos does not support nepali calendar they are planning to use 28 day for interest calculation on the min amount).

So for the Posting functionality here are some options

1. A batch job is used to update the "NEXT_INT_POST_DATE" to the correct date. (However i still have to dig into how exactly this functionality works for dates that are not end of the month) .. see spec http://www.mifos.org/knowledge/functional-specs/product-definition#savings
2. A button (action) is added on the admin tab to "post interest ". So when a user clicks on it, the interest is posted.
3. A Date field is added to the saving product definition where user will be able to enter the date for the next posting.. (however this may change from one fiscal year to next or every six months), so if the user updates this date once interest isposted, this change should be reflected on all exisiting instances of the product.