1. Put an inserter that activates on wire condition and a chest with items behind
2. Place a cargo wagon at the front
3. Turn on the wire signal to activate the inserter
4. Turn off wire signal, remove cargo wagon - try this or an opposite order to make some of inserters stuck with item in hand - that's ok
5. Place another cargo wagon - stucked inserters finish their swing placing an item when circuit expects them to stay turned off.
Same for filter inserters - they finish their swing when cargo wagon is available even if their filters are set to a different item (not which they have in hand).
On this screenshot these stucked inserters will finish their swing as soon a cargo wagon is placed at their front regardless of circuit signals:
