Managing boil-off

I've been doing DeathBrewer's stovetop AG method for a couple of brews now, but my equipment is a little inadequate -- I have a 5gal and a 3 gal pot, so after mashing & sparging I've been topping up to boil volume and splitting the wort into the two pots. This allows me to do a full boil, but it makes for a pretty high boil-off rate. So, I'll be adjusting my boil volumes to compensate, but I'd like other suggestions on how to handle boil-off too.

A few ideas I have are covering the pots during the boil, but this has pretty obvious risks, or adding extra boiling water during the boil process to keep volumes high. I know I could always do post-boil top-up, but I'm trying to keep costs down as much as possible so I don't want to lose hop utilisation too much.

Thanks!

What i use to do when my boil pot was to small for a full boil was to collect ALL the volumn that i needed. I could only boil 6 gallons safely so i would start my boil and periodically keep adding wort to the boil as time went by. I figured out that i needed to add about 1.25 gallons to my 6 gallon starting point, that would get me to about 5.25-5.5 gallons after cooling.

Just make sure to have all your wort in the kettle for at leste 15 minutes of boil time to kill any bacteria.

Thanks!
Would that process have any negative effects in terms of hot break from the newly added wort, etc?

Yeah you might have some more hot break once you pour in the topoff but that can usually be managed fairly easily. I dont believe i ever had any problems with that process but that is just me.

How much can you safely boil and what amount are you trying to end up with after cooling? I usually try for 5.5 gallons