Unfortunately, you can not fix a broken leg from hom. If the leg is not properly set, it might cause the dog permanant pain for the rest of their life. You do want to keep the dog inactive as possible until you can get him into the vet. Some vets have funds to help with vet care in emergencies like this. In additon, perhaps the following organizations can help.
Help-A-Pet http://www.help-a-pet.org/ This group helps low income families with vet care. IMOM http://www.imom.org/ This organization help people with emergency medical care in some cases. Care Credit http://www.carecredit.com/ Quick application and approval for care credit card. You can sometimes apply and get approval while you are at the vet office. American Animal Hospital Association http://www.aahahelpingpets.org/home/ Helps animals that have been abandoned or if the owner is having financial hardships Angels 4 Animals http://www.angels4animals.org/ This organization offers financial aid or treatment to those pets and owners in need. God's Creatures Ministry http://www.all-creatures.org/gcm/help-cf.html Help pay Vet bills for those that need help The Pet Fund http://thepetfund.com/ Helps provide emergency vet care to those in need. United Animal Nations http://www.uan.org/lifeline/index.html They help rescuers, low income and homeless pay for vet care
I wished there was more that could be done. I can't even recommend aspirin for pain relief at this point as there may be bleeding and it may interfere with medications needed to fix the leg. .