Looking at a family trip to South America and have some questions about the EZE/GIG flights.

After some initial confusion I got my head around the fact that LHR-EZE is in fact LHR-(RIO)-EZE, like the SIN/SYD flights.

Is an Amex 241 Avios routing possible MAN-LHR-EZE, then EZE-RIO (few days layover), then continuing RIO-LHR-MAN on one ticket so that we can have a multi-stop trip on one booking and maximum use from the voucher?