Your options are basically limited to;
- Changing the composition of the impactor.
- Changing its velocity (higher equals more friction) .
- Changing its size/volume.
- Changing the angle of entry to the atmosphere
Or in reality a combination of any these factors.
The kinetic energy released by an object hitting the Earth is basically governed by its mass and velocity. However density/structure is also an issue.
Comets are icy bodies originating from the fringes of the solar system and composed of light volatile frozen gasses and dust. Consequently the don't have a lot of structural integrity.
Asteroids on the other hand are left over rubble from the formation of the inner solar system and come in three basic types based on their composition. One type consists of mostly light elements like silicon and carbon, the second is a mixture of the first type with metals added and the last is mostly metallic (Nickel/iron). Obviously this last is your worst choice in terms of a mid air explosion unless it is much smaller that the Chicxulub object. Think armour piecing bullet vs hollow point bullet.
Assuming they approach at the same speed and angle as the original impactor you would want a smaller and/or lighter object. A comet (or the remains of one) might be your best bet because it should have less structural integrity than a denser metallic asteroid of the same size which will retain its integrity longer and therefore is more likely to hit the Earth.
Angle of decent is important because a steeper angle increases the energy (shock of impact) on the object as it enters the atmosphere while at shallower angles the time it takes to travel though it before hitting the surface is marginally longer. Depending what the object is made of fractions of seconds would count.
So if you want it blow up before hitting the earth, make it smaller or alternatively less dense than the original and/or have it come in a slightly shallower angle so that it has more time to 'burn' on its way down.