Mitzvos tzrichos kavanah - bracha on maror

On 115b the gemara attempts to prove that "mitzvos tzrichos kavana" from the fact that if one uses maror in place of another vegetable for karpas, one must still do an additional dipping for maror to fulfill mitzvas maror. Rashi explains that since the bracha of "al achilas maror" is not recited by karpas, there is a chance that one will not have kavana for the mitzva of maror, and therefore it must be repeated. While many people recite "lshem yichud" or some other fomula before mitzvos to arouse kavanah, we see from Rashi that this is in fact on of the functions of saying a birchas hamitzva.