I'd like to have that too! For the exact same reason (full screen image viewing on a separate display while advancing the file display).
I use that hotkey code to get an emergency solution (you need to have two of these to also step back).
The hotkeys I use are +<Numpad +> and +<Numpad ->
[code]@nodeselect
@runonce
@runmode:hide
@filesonly
@sync
d:\bin\file\dopus\dopusrt.exe /acmd Select Next
@sync
d:\bin\file\dopus\dopusrt.exe /acmd show_external_nodeselect[/code]
You need this usercommand as well:
<?xml version="1.0"?>
<button backcol="none" display="icon" textcol="none">
<label>Show_External_NoDeselect</label>
<icon1>#usercommand</icon1>
<function type="normal">
<instruction>@nodeselect </instruction>
<instruction>Show</instruction>
</function>
</button>
Pay attention, DO in v11.7.1 crashs for me when using this method to browse images. And in case you hit something non-image, the external viewer will forget to use "fit to page".
Reported here: View size setting get's lost
Here's another hotkey which I use to rate the currently viewed image and advance, don't know why some use dopusrt.exe or "@sync" and some do not.
Seems I had problems finding the perfect solution, so be careful. o)
[code]@nodeselect
@runonce
@runmode:hide
@filesonly
SetAttr META rating:5
Select Next
@sync
d:\bin\file\dopus\dopusrt.exe /acmd Show_External_NoDeselect[/code]