Upgrading a heat pump to a larger heat strip
Hold on. This doesn't make any sense.  

You seem to be assuming that operation of the heat strip is a normal state of affairs and this is where your heat comes from on a 35-40 degree day.  No, no, that would be entirely pointless!  It would defeat the purpose of even having a heat pump.  At that point you might as well just have an air conditioner added to a pure resistive electric furnace.  

Something is wrong with your heat pump.  I know that's not what you want to hear, but the repairman will be cheaper than the electric bills all winter long from running resistive heat.  What an expensive way to heat!!!! 

I mean, if you really want that, you can just install a bunch of $50 Cadet style electric baseboard heaters at 2000 watts a heater, as many as you plese. Feed them from a contactor operated by the same 24V signal that kicks the emergency heat on. Easy peasy.  But you'll hate me when the bill comes. 

The only other possibility is that the heat pump was wildly mis-specced for your location, which needs to be hashed out with the installer if it's a new install, or the previous owner has just been living with for years.  But that seems insane; you have the worst of both worlds.  The maintenance expense of a heat pump system with none of the cost/efficiency savings.