What I would say halacha li-myse - לענ"ד המאד ענייה עד לכדי פתטיות - is that when doing mitzvos one should both PERSONALLY IDENTIFY emotionally, intellectually and spiritually with the mitzva. At the same time he should be MOTIVATED to do the mitzva and fulfill it with the intention that it is the will of Hashem. Thereby he gets the benefits of both heteronomy [following Hashem and being His eved] and autonomy ["feeling" the mitzva and fulfilling from a place of deep intense identification and not as a dry formalistic act] in his Avodas Hashem.
I would add [and I will because these posts don't cost me anything] that there is a mitzva di-oraisa of adopting Hashem's "qualities" of compassion, love, concern etc. etc. So if one, for example, gives tzedaka and feels no kinship or care for the receiver but does it with the same excitement that we do Pesach cleaning - he has nullified the mitzva of והלכת בדרכיו. So the heteronomy demands an autonomous fulfillment of mitzvos [at least the moral ones]. So Kant would at least be happy about that. Not that I have nothing better to do on a Sunday morning than worry what a German philosopher would think about mitzvos....
