You flat out can't do this in a stored procedure. There's no way to create "dynamic" SQL in a pre-compiled object like a stored procedure. In point of fact, there's no way to take a constructed string value and invoke it. There simply is no function/operator/whatever to do such a thing.
You're stuck with SQL views (whose construction you could automate to some degree) or using a full-blown programming language. It's rather unclear why you need something more "dynamic" than a SQL view. Perhaps you could maintain the table definition and its companion extraction-to-Oracle view in the same file. But, and here's where the news gets worse, I don't believe you'll find that you can use BCP to extract data from a SQL view anyway. So what you might need would be a bulk-copy-from table that contains only the columns of interest (truncate it when you're done moving data).
One thing that may help you remember the limitations of stored procedures is that every table name and column name that appears in a stored procedure must be represented in the compiled code by that table & column's ID from (respectively) sysobjects & syscolumns. Or, to slightly oversimplify, this is the whole point of a stored procedure: to avoid the cost of compilation and optimization on a query that otherwise would be resubmitted each time.
So, if you can't type in the SQL as a (relatively) simple query, you can't do it in a stored procedure. You can't generate SQL which you then invoke within a procedure. Just as you can't do this by hand without taking the results of a query and pasting them back into the query window and invoking it yourself.
Another approach you might consider is that Oracle can read directly from Sybase with the appropriate middle-ware. That might be the most effective approach in the long term. Sybase could also insert the data directly into Oracle's tables (another fairly simple option).
At any rate, sorry if this is discouraging, but the approaches you have in mind are not possible options.
Best of luck,
J M Craig
Alpha-G Consulting, LLC
nsjmcraig@netscape.net