"Quick Stock Entry" makes it as easy as just typing in the symbol and pressing <ENTER>, assuming you want to use the same route (SMART) for each. Search for it in the IB manual.
You can manually edit the jts.pg file, but it stores a key value, not the symbol itself, so you'd have to create a map of known key values against symbols, write something to look up your symbols and spit out the key values, hope they don't change (they don't seem to), etc.