Can a parameter be passed to embedded sql that uses an EOF ?

I would like to pass a parameter to the following code that uses an EOF

sqlplus username/password "Sample Text" <<EOF

prompt &1

select '&1' from dual;

exit;

EOF

However it does not seem possible to directly pass the parameter. The only workaround I have is to separate the code out to a separate script rather than use EOF embedding ( however I actually need to use this EOF embedding ) eg this workaround works but as above I need an EOF method

sqlplus username/password @myscript "Sample Text"

myscript.sql

=========

prompt &1

select '&1' from dual;

exit;

Has anyone any ideas on how to pass a parameter directly into the EOF method ?