you can do this already, believe it or not

but yes it is very hard to figure out how since it's such a weird thing.
the funny part is that you already figured out how to do it with your first example

to learn more, go to the help file, and the section Advanced Use -> Using Alias Action Keywords:
A new feature with FARR version 2 is the ability to specify alias names in your search string using the + prefix (just like keyword modifiers).
When an alias name is specified in this way, anywhere on the search string, it does not effect search, but it will cause the alias results to be displayed AFTER the result file is selected, with the selected file name as argument $$1 in the alias.
In this way, you can perform a normal file/folder search and then launch a specific alias command with that file/folder as an ARGUMENT.
For example, you could create an alias named +hexedit
whose result contents are:
C:\Program Files\HexEditors\HexEdit.exe "$$1"
Now you can type in your search:
+hexedit mydocsearch...
As you type mydocsearch words, FARR will let you search for files as normal.
After you choose the result, instead of launching the result file, you will be presented with
C:\Program Files\HexEditors\HexEdit.exe "SELECTEDFILE"
Which you can then launch.