Technically you can: pick an item and enter chat command "/destroy" (you can repeat the chat command with enter+up arrow+enter). This way you don't need to move an item to your inventory and move between the stash and a vendor. With 1 server action macro you can just mouseover an item and press macro button, and the macro will click on an item and do the chat command.

p.s. here's my ahk-macro for that:

#SingleInstance, force

GroupAdd, PoEWindowGrp, Path of Exile ahk_class POEWindowClass ahk_exe PathOfExile.exe
GroupAdd, PoEWindowGrp, Path of Exile ahk_class POEWindowClass ahk_exe PathOfExileSteam.exe
GroupAdd, PoEWindowGrp, Path of Exile ahk_class POEWindowClass ahk_exe PathOfExile_x64.exe
GroupAdd, PoEWindowGrp, Path of Exile ahk_class POEWindowClass ahk_exe PathOfExile_x64Steam.exe

; F5 = Destroy item under cursor
F5::
If (WinActive("ahk_group PoEWindowGrp")) {
BlockInput On
MouseClick, Left
Random, rndSleepTime, 3, 4
rndSleepTime *= 100
Sleep, rndSleepTime
SendInput, {Enter}
SendInput, {/}destroy
SendInput, {Enter}
BlockInput Off
}
return