No alternative.
I argued that since I am able to select from a number of currencies in which to pay for an online booking, I should be able to use the voucher in that selected currency. But no go. I should add here that MH take 7% commission in currency exchange, but they still won't do it for vouchers.
I also argued that the following T&C: "the MH E-voucher is without any route restriction. It is applicable for Malaysia Airlines and MASwings operated flights, Codeshare & Interline Partners flights that are available on the website." is in contradiction to the use of only the voucher's currency, as there is only 1 route in which I can use it. But again, no go.