Useless advice: You don't need this to beat the game.
However, if you find a way to edit the values of the NPC, this may work. You should use some proto editor to open the file that contains your NPC's stats for the last level, then open all the other files for the same NPC, and edit them to make them the same. This way, from its first level your NPC will have the same stats as any other level, equal to the stats at the last level. I think it's going to work perfectly if you start a new game. However, I don't know about if you continue from a savegame.
Here's another idea
Step 1: Save a backup of your game.
Step 2: Find out which is the file for the last level of your NPC (you may experiment with all of them (by choosing a random one and proceeding to the next step) until you find the correct one, look for how much HP your NPC should have in a site - like per's walkthrough). I don't know where exactly in your Fallout 2 game directory are those files, and I can't check, since I don't have Fallout 2 installed here.
Step 3: Copy this file somewhere else, then rename it like a file that represents the NPC at another level. Then copy it again at the same directory, and rename it like another file that represents the NPC at another level. This until you have it for all files. Then move your newly created files to your proto directory, and overwrite your old protos. This way, you should have the same file for all the NPC levels.
Step 4: Do the same thing for all your NPCs.
After this run the game and see if it worked. Do this at your own risk. I think the worst that may happen will be fixable by a reinstall.
I think that you may not be able to find all the proto files for your NPCs in your folder that contains proto files. In this case, you need to extract them from your master folder, using the appropriate tool - I think you need a .dat explorer. However, I don't know which files are for the NPCs. I think this is obvious by their names.
You can find all the files you need here, on NMA.
Also, I don't guarantee that this approach is going to work. But trying won't hurt.