Note that you can statically locate sepcific variables in the XDATA memory region without using a heap and any call to malloc(). You just have to specify the relevant storage keyword (not sure what it may be for IAR, but most probably xdata, _xdata or __xdata) when you declare the variable.

If you didn't need to use specific libraries with your platform, then the cheapest route would be to code in C with the sdcc compiler. But your specific target might require you to do a lot own own work to be able to map all hardware and to recreate helper functions that you may have received with the original kit.