I’ve found this nice solution for double cues but my requirement has the additional intricacy of combining two voices in a chord-like fashion, like so:
Currently Dorico separates the cues by parts; forcing the stems in any direction doesn’t combine them. Would it be possible to create something like in the image without major trickery (like a separate player)? And if not, maybe consider this for the future?
I’d imagine this is within the remit of Condensing, the feature that hasn’t yet appeared in Dorico but is planned for a future release. This feature will theoretically combine multiple individual trumpet staves (for example) and show them as one stave in the score whilst maintaining multiple trumpet part layouts. My supposition is that, having done that, you’d just go Shift+U and type/select Trumpets 1,2.
I think being able to cue a condensed player is probably going to be a whole 'nother ball of wax, so I wouldn’t expect that in the initial implementation of condensing.
A separate player is the way to go for the time being.
Ah well, consider that a feature request, Daniel 
Yes please. I know this thread is old (do forgive me if this has already been implemented), but combining, say, violins, violas and cellos into a single ‘Strings’ cue would be a Godsend.
Leigh, you could cheat this by having a separate Strings stave that doesn’t show in the score. Condense your desired string cues into it, manually, then cue it wherever needed.
Good plan Leo, thanks!