If I have no money or assets to contribute now what are my other options?

You could be a potential Wakif through planned giving; by writing a will (wasiat) to bequeath your asset i.e.from the sale of your HDB flat after your demise.

However, if you have inheritor(s) or heir(s) to your assets, only up to 1/3 of your asset(s) are allowed to be bequeathed as a contribution. This is in accordance to the Islamic ruling of Faraidh.