The best way to back up a DSL without cable is to get some sort of dialup connection. That is what I currently do, not because of the added expense, but because it is the only sure way to know that I can access my broker if the DSLAM to my DSL goes down.
Unless you are monitoring/trading many many symbols, the speed of the dialup will not adversely affect you for the few minutes/hours/day that you need to worry about it a year.
nitro