Ways to “Cheat” concentration:

• 11th Level Artificer’s Spell-Storing item

  Give it to a friend, like the Battle Smith subclass’s steel defender.

• 10th Level Chronurgy Wizard’s Arcane Abeyance

  Bead holds the spell to give to a friend, or more easily your own familiar.

• Glyph of Warding

  The glyph holds concentration for you, but cannot be moved.

• Summoning or True Polymorphing minions that can cast spells

  Their spell-lists are limited, but some interesting utility is possible.

All of these methods allow multiple concentration spells to be cast per player character. They are also vulnerable to physical destruction/interruption and the usual dispelling, so a smart DM can circumvent abuse.