private relay ... could i use srs to avoid spf fail?

hi folks,

i would like to provide a private SMTP relay so anyone (with any email 
address) on a particular network could use this SMTP server for outgoing 
mail.  We can assume that this server will never be listed in any 
domain's SPF records.

i think (please correct me if i'm wrong!) this would cause spf failure 
.... if [email protected] is using SPF on domain.com, this would cause 
spf failure if delivered via my relay

i wondered if i could use srs to get round this in some way .... treat 
each email as if it were being forwarded from the server's default email 
address insted.  does this sound feasable? if so, am i right in thinking 
that the final recipient would see the 'tagged' srs address as the 
'from' in their email client?

thanks for any thougths

ap