I have had an echophon and a tapographic. I think what you are talking about is clocking the delay, literally, from your swung clock. The echophon turns that into a really nuts warble because itâll be constantly trying to average the speed (as you have noted).
I believe (but I will have to check) that the tapographic will also do that if you try to clock it using your swung clock. But if you just set the loop length of the tapographic using a tap (or a different divided non-swung clock) you can then insert additional taps at swung beats or at whatever interval you like. Youâll still probably want to have the overall loop set at some multiple of the bar you are swinging.
And as others have noted if you set the loop at some multiple of the bar, the delay will probably still sound pretty swung because you are feeding it swung pulses. (So, if you just set the loop/time on the echophon by ear, you might get a pretty good result, too).