reading numbers as symbols

[hunter@ncbi.nlm.nih.gov (Larry Hunter)]

I'm fishing for zip codes in large email files, and I would like to read
preserving leading zeros in numbers.

I wrote a function that looks for potnums in strings and puts || escapes
around them.  It works, but it is inelegant and inefficient to have to read
strings, then escape the potential numbers, then read-from-string.

I would prefer to get the reader to treat all tokens that are potential
numbers as symbols.  Something like setting the *read-base* to 0 :-).  

Is there some straightforward way to do this that I missed?

Larry