Is there a way to boost polymorph concentration

So - say you cast polymorph on yourself at lvl 7 and make yourself a giant ape. Aside from using bless on yourself 1 turn prior - is there any way you (or someone else) can either

1. Increase your constitution to give you a stronger chance of maintaining your concentration when attacked 

2. Gain advantage for concentration checks when attacked 

3. other ways to raise that concentration when attacked 

There isn't much of anything you can do for yourself:

• You don't get any of your character abilities while under the effects of polymorph, so you can't use things like war caster or resilient.
• You don't get benefits from equipment, so no items that boost constitution saves.
• Every spell effect that I know of that gives bonuses to concentration (including bless) requires concentration, and thus can't combine with polymorph.
• Something like a potion of heroism might persist, ask your DM.

Bonuses from allies work normally, so things like bardic inspiration, aura of protection, and spells cast by allies can apply.

If the circle magic options from the Forgotten Realms are permitted by your DM (which many might not - they’re fairly poorly designed), you could circle cast using the distribute option so a second player can help maintain concentration if yours drops.  

I mention this because it is responsive to your question, but highly recommend you do not even consider asking anyone else to do this for you. It is not exactly great in a cooperative game to ask someone to sacrifice their turn and concentration so you can do something cool by yourself, and this option is really better suited for things like Pass Without Trace, where the entire party benefits.

Actually pre existing spells are still permitted according to the rule book - even if concentration 

Bless and polymorph are both concentration, so you can’t bless yourself then polymorph, the bless will go away. You’d need an ally the bless you. Thats how pre-existing spells might stay even if you change form. Polymorph does not allow you to maintain concentration on multiple spells at once.

I was going to suggest enhance ability (from an ally) but that specifically does not allow constitution.

Quote from Xalthu >>

Bless and polymorph are both concentration, so you can’t bless yourself then polymorph, the bless will go away. You’d need an ally the bless you. Thats how pre-existing spells might stay even if you change form. Polymorph does not allow you to maintain concentration on multiple spells at once.

I was going to suggest enhance ability (from an ally) but that specifically does not allow constitution.

Enhance Ability only benefits ability checks anyway. (Which is probably why they took out Constitution in the 5.5e version, since Constitution ability checks pretty much never happen.)