Very Late IBU Boost?

I've got my house amber in the keg and slowly carbonating in the fridge. It's got at least another week or two before it's drinkable.

Problem is, I took a sample and it's super malty. I was trying to balance out my recipe IBUs and looks like I went too low. Right now I'm guessing that it's around 17 IBUs when it should be around 25.

What's the best way to add 8 IBUs to a brew that's kegged and carbing!?

I can think of the following:

1) Boil a small amount of water with some hops to add (worried about thinning my brew).

2) Extract some beer and boil that with hops (worried about alcohol flashing off and just tasting bad)

3) Pour in a couple bottles from a previous batch that was overly-hoppy (probably around 40 IBUs) - not sure if this will be enough to do anything.

4) Dry hop (no IBUs but could help cut the malt flavor a bit)

Any other techniques or suggestions?

I vote dry hop, which at least will add some hop aroma.

If you want bitterness, I'd say make a hop tea, (boil in water, etc.). Or buy a hopshot and boil that, (hopshots still need boiling to isomerize).

See this thread for an alternative: isohop-hop-extract