I guess the only way to find out would be to measure your SG....I'm not sure how unboiled wort would effect the gravity, if at all? I'm assuming by asking the question you know already that >1.050 SG wort needs more hops.....so thats my only guess (a poor one at that!), if you can't measure the gravity of the combination, you must be able to average the gravity between the two seperately, and use the (WG - 1.05)/2 formula and add accordingly?

Unless you are adding a lot of wort to the boil, I would say it would be miminal.

How much are you talking about adding?

Utilization is affected by boil volume and gravity. The bigger the volume and the lower the gravity, the better the utilization. That's why it is always best to do full volume boils.

I have tried what Jake is proposing, and my utilization was terrible. I would suggest making smaller batches or getting a bigger boil pot.

This is what I was doing:

Collecting 6.25 gallons in a 7.5 gallon pot, and then collect another 1.25 - 3.75 gallons in a 5 gallon pot. I would do at least a 90 min boil, only adding hops to the 7.5 gallon pot, and topping it up with wort from the 5 gallon pot every 15-30 minutes.

Whether it was a light wheat beer or a barleywine, they were all too low in bitterness.