There is nothing you can spray that will kill just the Hairy Bittercress without also killing the Blue Star Creeper. Mechanical removal is the only way to stop it.

The active ingredient clopyralid is designed to selectively kill broadleaf weeds 'over the top' of many landscape ornamentals....as well as edible crops (on different labels.)
It is sold by Dow, under the trade name 'Lontrel'.

http://www.dowagro.com/turf/prod/lontrel.htm

I've used Lontrel for years !
I just love it, especially for over-the-top control of Canada thistle...that seems to 'pop up' through everything that I buy "balled and burlapped" from any nursery around here.
(huh...go figure !)
( ;

But you won't find this at any of the box stores !
You have to go scour around places where LANDSCAPERS buy their chemicals !

Also...
'Over-the-top' control for quite a few GRASSY WEEDS growing directly 'through' bushes and ground cover in the landscape
...would call for FUSILADE II from Syngenta, purchased from some of these same places.

http://www.syngentaprofessionalproducts.com/prodrender/index.aspx?prodid=344

Don't be surprised, though, if the qt containers of Lontrel & Fusilade are somewhat a too expensive for what 'Joe Homeowner' would use in 1 or 2 years...they're CONCENTRATED, and designed for the 'pros'.

But... there's NO law saying homeowners can't buy them from any vendor...because neither product is a restricted-use pesticide in any state.

However...almost all vendors reserve the right to CHARGE homeowners more for these products, than they do the professionals. (The reason for this is obvious.)

A homeowner with a decent piece of landscaping to maintain would just have to think 'long term'... and suck-up a little on the price, and of course, keep it away from the kids and pets, and keep it in a place where it wouldn't freeze in storage during the winter.

Because of the hazards posed by clopyralid it is a Restricted Use Herbicide, meaning that only licensed applicators are supposed to be able to get and use this extrmely toxic product. This is not something the average homeowner would want to use.