Hi,
I juste added some preliminary support for FlowSpec (RFC5575) to my BGP route injector http://bgp.exa.org.uk/
As I am not aware of any other project allowing to inject flow route into a network, I am taking the liberty to plug it here.
You can access the SVN repository at: http:/svn.exa.org.uk/bgp/trunk/ the code is under a 3-clauses BSD licence.
More information about the installation are available on the wiki.
I performed basic testing by rate-limiting one of my coworkers mail and web flows - seems to work - for the rest, it may not do what it should.
If you are interested, have any questions, or are missing a feature, or just find any bugs, please, just let me know.
Changing the configuration and sighuping the application perform send the peers the correct update messages to change the peer RIB.
Or just enable graceful-restart and restart the application if you do not care about the number of update 
More information:
- http://www.terena.org/activities/tf-ngn/tf-ngn17/uze-flowspec.pdf
- http://resources.nznog.org/2006/Friday-240306/DavidLambert-BGPFlowSpecificationUpdate/Lambert.ppt
- http://uknof.org/uknof15/Mangin-NakedBGP.pdf (another shameless selfplug - BGP overview - 3 slides on FlowSpec)
Thomas