ICUS is a funny fish, and I reckon a lot of people (me included) have logged ICUS that wasn't exactly ICUS. And I don't mean intentionally either - but that happens too.
If you don't have your 90 day recency, but still hold an unexpired instrument rating, I would have thought you could do exactly as Zapp was suggesting. For CAR 5.40 as per Lasorhinus's post, you do in fact hold the rating. You can't act as PIC under the rating, due to recent experience requirements - but you hold it, until it expires.
But I can see the other side of this arguement, as per what Lasorhinus has said... Is this another case where "precident", or "accepted practice" in the industry is decisive (or which CASA office's jurisdiction you're under!)
Let me pose another hypothetical, to "support"
my argument:
What about having your required general IF recency, but no ILS in the last 35 days... Then you go out, get a practice ILS when able (even on IFR revenue ops, and single pilot) and as long as you're not in IMC below MSA on the approach, you can fly it, log it - and now you can fly ILS's in IMC again for another 35 days - or can you not do that either?? (We do this when required, though usually you catch it before you actually expire, so subtly different).
Interested in anyone's ideas on that, and the differences between the two if any.
Cheers,
CR.