I'm not sure I agree with the addition of sugar to replicate the flavour of tamarind. Tamarind has a somewhat tart, sour flavour, it's not really sweet. It's a souring agent.
When I use tamarind, I use the dried blocks and break a part off, soak it, strain it and either use the liquid or reduce it to a thick paste.
I've also found that a few dashes of Worcestershire Sauce can impart a tamarind-type flavour without introducing any sweetness. After all Worcestershire Sauce does have tamarind in it, amongst other things so it may be a more convenient substitute.
I've used Worcestershire Sauce in a number of Indian dishes in this way with quite good results. I also cook beef rendang, but I've never used tamarind in it.