Hi, I run exactly hte same heater on exactly the same filter with no issues. However, due to the ribbed piping, I have hung the heater from a nail to ensure it doesn't work loose.Changing the pipes however will be a better option! Obviously the flow will be reduced a bit too, but I expect you realised that anyway!
Was reading about this too and somewhere there was mention that placing things inline on a Fluval was not a good idea.
Something to do with the hose clips on the filter itself poping out, but I haven't tried so can't say its true, either way I am going to get a Tetratec EX1200 instead.