There is no command that uses items, only assignment is possible. It's not possible with a single press, but it can be achieved by pressing the same button three times.

Below is an example of a macro that sets an item into its own hotbar slot. Two additional presses are required after execution. It may be possible to shorten the wait time (in seconds). Assume that hotbar 2 is not shared, and this macro is assigned to slot 1 of that hotbar. Adjust the hotbar and slot numbers to fit your setup.
Caution: This will overwrite shared hotbar 2.
/macrolock
/hotbar copy current 2 share 2
/hotbar share 2 on
/hotbar item "Pearl Chocolate" 2 1 <wait.2>
/hotbar item "Gysahl Greens" 2 1 <wait.3>
/hotbar share 2 off
/companionaction "Healer Stance"

This is a slightly modified version of a macro I posted in a past thread:
What's a Macro for Phoenix Down?
I referred to the "Message Macro Type ASWC" in Macrology (Third Edition).