You can use any carvariation for this but i will be using MPChristmas2 

go to update>x64>dlcpacks>mpchristmas2>common>data

under the line which says   <variationData> paste the lines below
ENSURE YOU DO NOT DELETE THIS <variationData> LINE OR THE NEXT ENTRY OR YOUR GAME WILL CRASH 

<Item> 
<modelName>policeb2</modelName> 
<colors> 
<Item> 
<indices content="char_array"> 
134 
134 
156 
156 
</indices> 
<liveries> 
<Item value="true" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
</liveries> 
</Item> 
<Item> 
<indices content="char_array"> 
134 
134 
156 
156 
</indices> 
<liveries> 
<Item value="false" /> 
<Item value="true" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
</liveries> 
</Item> 
<Item> 
<indices content="char_array"> 
134 
134 
156 
156 
</indices> 
<liveries> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="true" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
</liveries> 
</Item> 
<Item> 
<indices content="char_array"> 
134 
134 
156 
156 
</indices> 
<liveries> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="true" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
</liveries> 
</Item> 
<Item> 
<indices content="char_array"> 
134 
134 
156 
156 
</indices> 
<liveries> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="true" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
<Item value="false" /> 
</liveries> 
</Item> 
</colors> 
<kits> 
<Item>157_massacaro2_modkit</Item> 
</kits> 
<windowsWithExposedEdges /> 
<plateProbabilities> 
<Probabilities /> 
</plateProbabilities> 
<lightSettings value="1" /> 
<sirenSettings value="13" />
</Item>

Thats it :D you can now have both bikes