I would say there's a lot of augmentation, even without Astartes implants, that you can do to the body. Look at the non-Space Marine 'Space Marines'; Luther and Kor Phaeron. Both of whom were too old to recieve the implants but were given some level of augmentation and still stand head and shoulders above unaugmented humans.
This seems borne out further with the example of Lord Hector Rex. He had augmentations and is a massive individual, much more physically powerful than a normal man. In the Soul Drinkers series there was an Inquisitor, again very imposing being very tall and strong, wearing power armour. He reminisced that while he didn't have the implants and advantages of a Space Marine he was superior to normal men and his operations whilst agonising, were worth it for the intimidation factor.
So evidently yes, there are ways for Inquisitors with suitable pull, who know the right people or organisations to become physically superior. It's going to differ on a case by case basis of course, given the different levels of influence and methods of each individual Inquisitor.
Also bear in mind the enhancements done to Imperial Assasins, who are if anything even more deadly than Astartes, and who again lack the Space Marine implants. Though their training no doubt plays a large role in this.