Is it bad practice to place a bypass capacitor under its respective component?
In many cases its the only practical way to design the board.
For example with a large BGA package the opposite side of the board is the closest place to put a capacitor to most of the possible power pin locations.
That said, 0805 is really quite large. 0402 should be hand solderable if you are in good physical shape (no hand tremors) and have good eyesight or a magnifying glass. 0603 should be hand solderable without magnification unless you have an uncorrectable vision problem.