Using larger pipes is not expensive, having a bit of an awkward run to take the route internally is not that expensive, if required insulating the pipe with trace heating is not that expensive.
I totally agree with using larger pipes & insulation externally and with awkward internal runs.
I disagree with unfeasible or impossible internal runs.
As for trace heating. I'd be f***** if I'll introduce another needless piece of sh*t to breakdown into the deal. Rather let someone else have the job.
How can it be needless if it prevents the condense from freezing and stopping the boiler from working, leaving the customer cold in these extreme conditions, so you would rather the boiler breakdown, rather then add something that could prevent this.
If I find a route internally, it would not be impossible and if it saves on insulating the pipe, or using trace heating and preventing the condense from freezing then it is not unfeasible.