All you have to do is ask. 180 till 10 and 160 till 4 is not a problem.
We do, as I'm sure you well know.
The problem is that, on all too regular a basis, these speeds are not complied with. Almost every shift that I have done recently, at least one a380, having read back the aforementiond speed requirement, is found to be doing 135 knots or so, 6 or 7 miles out (asked and confirmed, not just observed groundspeed). Furthermore, no-one seems to think it's worth telling the poor atco who is about to be suspended for losing separation!
I've said it many times on these forums and I'll repeat it again - if you can't comply with the speeds, PLEASE at least let us know. That way, we'll make allowances with the guy behind. Otherwise, someone is going around and I really don't see why it should be the guy who IS flying the speeds.