Yes, there is and very easy to do
I tried following and it worked for me, this is one of my Mysql profile
let g:dbext_default_profile_live_export =
'type=MYSQL:user=clear:passwd=`cat /Users/username/src/test/pw.txt`:dbname=abc
Just "cat" the file contains the password when you define the connection.
Now, I don't need to worry about others seeing my mysql user password from command line anymore.