Hi,
It sounds as though your heatpads are going to be different sizes (and therefore probably wattages ) so no they would be unlikely to be the same temps when connected straight to the same thermostat. That could make it difficult to get things right however.
You could, however, connect the cooler side heatmat through a rheostat and then connected to the thermostat. It will take a fair bit of tweaking and adjusting then waiting to see how it works out before you could be happy it was set up right though.
I would second tigerlilly's suggestion of insulating the tank first to see how much difference that makes.
You can get herpstats that can control different heaters to different temperatures if you can afford them. I don't know if they make helix's that do the same I'm afraid.
I am always a little squeamish about having the entire bottom of any enclosure covered with a heating element just in case anything goes wrong - perhaps anyone else could chime in on this?
Oh and definately don't tape anything inside the tank unless you are using low tack painters tape - the risk of injury if the snake gets stuck to regular tape just isn't worth the small amount of effort needed to find another method.
You would be better leaving the probes mobile rather than fixing them as you can then check the temps inside the hides on top of the substrate as well without having to buy anything else or tear up the setup.
dr del