Unfortunately there's no official rule that says you can do this.

In a home game, it would be fine. You'd talk to your DM and explain that you can't wear this armor as a barbarian, but that you'd like to just wear some of it and count is as half plate. Most reasonable DMs would issue a house rule saying you could wear some of the armor, just as you're suggesting.

However in Adventurers League you can't really do that. You'd have to ask each DM you played with to issue this house rule for you, and inevitably some of them would say "no, I don't want to deal with house rules at my AL table", and then you wouldn't have a good set of armor to wear during that adventure. It doesn't seem like it would be worth it.

I recommend trading the armor away to a character that wears heavy armor.

Unfortunately there's no official rule that says you can do this.

In a home game, it would be fine. You'd talk to your DM and explain that you can't wear this armor as a barbarian, but that you'd like to just wear some of it and count is as half plate. Most reasonable DMs would issue a house rule saying you could wear some of the armor, just as you're suggesting.

However in Adventurers League you can't really do that. One version of the AL DM rules says:

You’re Empowered. Make decisions about how the group interacts with the adventure; adjust or improvise but maintain the adventure’s spirit. This doesn’t allow you to implement new rules, however.

So the DM is not allowed to let you do this.

I recommend trading the armor away to a character that wears heavy armor.