David,

>I guess the programmatic approach would be to IMPORT the file then modify the resulting table structure with ALTER TABLE commands. Best I can tell, that's what the wizard does.

Just do programmatically what the IMPORT Wizard does, but using the commands

CREATE TABLE ...
APPEND FROM ...

For example:

CREATE TABLE mytable ;
(myfield c(6), myname c(25), mynumber N(12,2) )
APPEND FROM somefile TYPE DELIMITED [or SDF, or other types]