Yes. Find your keycommands_en.json file. Depending on your language the two letters before .json might be different. The file is somewhere in your AppData or Application support folder. Add these lines within the kStepTimeInput section. Replace X with your desired shortcut. Don’t omit the apostrophes and be careful not to break the json syntax!
{
"NoteInput.StartTupletRun?Definition=3:2" : [ "X" ]
},
The double click method doesn’t work with a shortcut, but you always have the end tuplet shortcut for that. (Instead you can easily create a triplet within a triplet within a triplet within a triplet… 
)
Hope it helps!