Named Parameters for SQLPLUS START?

I know that I can pass parameters to an SQL-script executed from SQLPLUS via the START command (or _at_). In my script, I have to refer to those command line parameters as &1, &2 etc.

Is there any way I can pass NAMED parameters, so that I don't have to remember that &5 was a tablespace name and &67 the spool file? Something like
SQL> _at_myscript user=emil tablespace=alb ?

At the moment, I have lines like
define user = &1
in my scripts, but that's not quite what I want.

Thanks a lot,

Martin

PS My opinions, not the company's!

-- 
Dr. Martin Ameskamp, AED Graphics AG
Mallwitzstr. 1-3, 53177 Bonn
Tel. 0228/9542-0, Fax 0228/9542-111
Email: ameskamp_at_aed-graphics.de