Keyword Filter: "Starts with" option

One use case, for a Twitter feed:

Filter out tweets starting with @ but permit tweets with @ in the body that don't begin with @.

Currently @ would filter in/out both of the following tweets when I want them treated differently:

@joe That's a good idea, thanks.
There's a delay on Church @ 17th.

In the meantime, a workaround is to precede the item with a regex filter that inserts an arbitrary string if the field starts with a particular string.

E.g.

REGEX to change /^@/ to /abcde @/
followed by excluding based on keyword abcde

(Assuming you're not going to ever use abcde in a field intentionally and want to show it.)

But that's a kludge and it would be better to be able to filter by beginning (and for the ability to use symbols, not just words)