You can use separate press and release keypress actions.
The most responsive way to do what you're describing is to use two separate commands, set to trigger from the same key, where the second command has the "Shortcut is invoked only when all keys are released" option enabled.
I.E. the first command, with the "Shortcut is invoked only when all keys are released" option disabled (unchecked), would contain
Press down NumPad 2 key
Press down NumPad 4 key
and the second command, with the "Shortcut is invoked only when all keys are released" option enabled (checked), would contain
Release NumPad 2 key
Release NumPad 4 key
You'll likely want to make sure the "Do not allow key to be passed through" option is enabled for both.