Pulling a dupe (or a would-be dupe in this case) indeed sucks. I'd be pissed too if I pulled a Yoshi right now, but that's just how RNG works. On the bright side though, you didn't necessarily waste energy. You still farmed gear and leveled champs- things you're supposed to be doing anyway to get stronger. 

I would be happy.  I would trade a blue shard for a lego book in a heartbeat.

This, So MUCH this!

I pulled every fusion except fro the one I didn't do : Maulie. 

- Brakus, Foli, 4x Harvest Jack, and the list goes on All the way to Astralon 1 day after I fused him !... moral of the story : I feel your pain, but your solution would only delay the RNG, it'll either happen or not no matter how long pulling the fusion from shards is held up. 

Another solution would be a possibilty to "sell" dupe legos and get something good in reward. There are suggestions about that from youtubers like Hell Hades out there allready. 

Now you can use your dupe lego as food (lol) or as skill book only for the copie. Even a lego book, that could be used to any champ, would be better.