[Serusers] Newbie question Best way to strip headers out of sip invites?

[Dale J. Robertson]

I am looking for the best way to remove headers from INVITES sent to my 
PSTN gateway. The invites from my UA are too long and return '513's when 
they include authentication. My provider doesn't support BYOD so getting 
them to change maxlength is not an option. there are several headers 
that are sent by my ua that are not sent by the ua they have provided. 
when I strip the extra headers out using textops subst function it 
leaves an empty line which the pstn gateway doesn't seem to like very 
much. Is there some other method to strip headers? or maybe my regular 
expression syntax is wrong? the re I use to select the Date: header for 
removal is '^Date:.*$' replaced with // . I am testing my re's using 
sed. I must admit I know nearly nothing about using regular expressions.
Thanks,
Dale