Maybe some boards lined with styrofoam to clamp it in vise but as stated above its probably not a very good idea.
Ive never assbled on myself but the way i understand that upper vise block is used to not only protect the upper but more importantly to allow the pressure to be applied to the "correct" areas on the reciever.
I dont see anyway around it cept to get the upper block and i dont think the savings are worth the risk. Plus if you just buy the right tools you will be able to properly assemble more in the future
