Smith Manoeuvre, RoC and interest deductibility

If you are executing the Smith Manoeuvre using ETFs that generate return of capital, the usual advice for ensuring that 100% of the HELOC interest remains tax deductible is to reinvest all distributions or use them to pay off the HELOC.

But suppose I'd like to move dividend income out of the investment account to use for other purposes while also reinvesting the RoC. The HELOC interest should remain 100% tax deductible. However this is complicated by the fact that at the time you receive a distribution you do not know exactly how much of it is RoC (normally you'd have to wait until you receive a T3 slip).

So what I propose is this: Based on the % of RoC in the ETF's previous distributions, pick a safe upper bound on the likely proportion of non-RoC income in the next distribution and move only that amount out of the trading account to use for other purposes.

Ex. If historically ~4% of each distribution is RoC, then transfer only 90% of each distribution out of the account when you receive it and reinvest the remaining 10%. This way you are very likely to be transferring only dividend income out of the account and not RoC. Therefore 100% interest deductibility is maintained.

Of course if you make a mistake and learn that, say, 11% of the distribution was RoC, you'll have to bite the bullet and accept that not all of your HELOC interest remains tax deductible. But by picking a sufficiently high upper bound on the non-RoC part of the distribution the likelihood of this happening should be very small.

My question is has anyone reliably done something like this? If I were to be audited by the CRA would they accept that the HELOC interest remains 100% deductible?