Exclusive Handover behaviour

Hi all,
This is a case of collocated BTS.
One of the BTS is city BTS with sectors ABC while the other is a highway BTS with sectors A&B.
The antennas of both are on the same tower but at different heights.
Height of Highway antenna B is 40m, BW=30, Azimuth= 240, gain= don’t know
The height of city antenna C is 30m, BW= 65, Azimuth =230, gain= 17dbi
Now what is the problem:
Let us say that the location of both the antennas is X
And let us draw a highway from X, like this
X——————–Y
Where the town is spread on both sides of highway up to the point Y.
After the point Y, we have this highway on which we need to provide the coverage.
But what is happening is that even in the town periphery between X and Y all the MS are doing C1 to highway BTS as the Rxlevels are stronger than city BTS.
All the traffic of city is getting passed through the highway BTS but I want that the city BTS should pick the traffic of city and after the point Y the highway BTS should serve.
How can I do this?
If I go for C2, that will be short relief as immediately after going the dedicated mode the MS will receive HO command to perform handover to highway BTS.
Do we have any option to define handover behavior exclusively among two cells ?
I doubt that if I modify the HO margin then the behavior of cell will be same for other cells also in its relation, that I don’t want.
What do you suggest?

regards

MKT