Tonight I tried the exercise bike, to see if it would torture my knees as the elliptical had two night earlier.
The answer is: Yes! Not as badly, but still enough for me to bail out after 45 calories (five minutes) worth of pedaling.
I went back to the treadmill and managed to run longer between walking and walked less overall. It all went fine. The stats, with previous run in brackets:
Distance: 4.38 km (4.22)
Time: 29:26 (29:35)
Average pace: 6:43/km (7:01)
BPM: 157 (156)
Calories: 327 (327)
Yes, even though I ran harder, had a significantly better average pace, I still burned the exact same number of calories. Or so my Apple Watch says. Perhaps it is a big fat liar. BPM remaining virtually identical despite the harder push was nice, though.