How i can subscribe to an Event through Inspector

Hi there!

I want to implement a simple feature for the editor, that able subscribe to an event through inspector object field. I will try to explain as much detail as I can.

Here is my code:

 [Serializable]
 public class SomeField
 {
     public UnityEvent onEvent = new UnityEvent();
 
     public void Raise()
     {
         onEvent.Invoke();
     }
 }
 
 [CreateAssetMenu]
 public class SomeExternalField : ScriptableObject
 {
     public SomeField property;
 
     public void Raise()
     {
         property.Raise();
     }
 }
 
 public class SomeMonoBehaviour : MonoBehaviour
 {
     public SomeExternalField externalPropertyReference;
 
     public void OnExternalEvent()
     {
         Debug.Log("OnExternalEvent");
     }
 }

Here is workflow
1. Create a SomeExternalField scriptable object;
2. Add SomeMonoBehaviour to a GameObject in a scene;
3. Select externalPropertyReference field in the SomeMonoBehaviour and choose the SomeExternalField from the assets;
4. In this moment i need subscribe SomeMonoBehaviour. ExternalStart() method to SomeExternalField.SomeField.onEvent event;
5. Enter Play Mode
6. Call SomeExternalField.Raise() and see "OnExternalEvent" in the console;

How i tried to find a solution
1. First that i do it was an Editor works. I wrote a PropertyDrawer, that used a UnityEvent.AddListener to subscribe. All works perfectly while Editor does not enter play mode, after that all subscribers were lost;
2. Yes, now i know that is AddListener is only works runtime and for editor need to use UnityEventTools.AddPersistentListener, but in my case it is impossible, because SomeField is not inherit a UnityEngine.Object;
3. I try to use standard C# events with delegates, but it works similar as 1st point;
4. Only one thing is working - initialise events on Awake(), but if some class will have a 10 or 20 "SomeFields", i will need to each initialise, this is ugly and so not practical;

Guys, I know my English is not very good and I hope that reading this topic will not cause you too much inconvenience. This problem has captured my mind and I can't get out of it.

May be someone faced a sort of problem and knows how to solve it or say that it is very difficult to implement and it is not worth it, that I would not get stuck at this point and continued to work further.

Thank you!