While I don't have an equation for you, I thought I would just ask for\provide some clarity. The temperature dependence is how much CO2 the beer will hold in solution. The amount of CO2 which is created is dependent only on the mass of sugar fermented by the yeast.
Thinking out loud....
From BeerSmith I estimate that you are targeting 2.6 volumes for a Cal common. This corresponds to 13.36 psi at 40 deg F. So we need to know how much sugar the yeast will need to ferment to achieve the proper priming. Now, for the last hour or so I've been loocking at chemical equation, ideal gas laws and molecular masses. However, I've come to think there is a much easier way. BeerSmith will tell you that for each gallon of beer at 40 deg F you would want to prime with 0.611 ounces of corn sugar. So all we need to do is calculate when there is that much fermentable suagr left in the fermenting beer. I used
this table for most of the calculations that follow. Using excel I was able to determine that each "point" on the hydrometer corresponds to 0.356 ounces of sugar per gallon. So if for each gallon we need 0.611 ouncs we would "seal" up our fermentor with 1.7 to 2 points left in fermentation.
0.611/0.356 = 1.7163
So if you expect that your fermentation will finish around 1.012, you would bottle at around 1.014. If I have done everything right, the "equation" becomes:
Estimated Final Gravity + (Required Priming Suger in ounces)/(0.356 ounces/"point") = Bottling Specific Gravity
I hope someone can double check this for me, and if you do end up using this approach, let me know if it works.