You can forget about them. thats probably your best bet. youd be better off doing some serious calisthetic movements then using 3lb dumbells.
im a gymnast, so if you want some help putting together a bodyweight training program id be glad to help.
to give you some ideas
Consider
Deep explosive pushups... explode up as fast as possible. Can you do more than 15? put on a backpack and fill it with stuff untill you can only do 5-10 and then work your way back up
Chin ups... slow negatives are best with these.
And if you got a chin bar you could hang off of it with your feet and do inverted sit ups. or leg raises.
Also consider working on your flexibility around your trunk, and hamstrings. if you can fold yourself up in two you have accsess to the greatest abdominal exercises known to man. 99.999% of people dont have the option of doing these simply because they dont put the effort into gaining the flexibility.
how about some tricep dips between chairs, again with the backpack full of weight
handstand pushups against the wall
Try this one for your shoulders, abs, wrists. Put your feet on a chair, and support yourself with your arms straight, and then lean forward as much as possible, try and get your center of gravity (usually your waist) overtop of your wrists. and hold for 5 seconds, repeat ten times for three sets.
Theres hundreds more but those are the simple ones.
but really man, get a power rack.
whatever you want to achieve thats your best way to do it.