A sudoku with 42 "unique" solutions?

This sudoku has 42 "unique" solutions, 1 of which will be chosen by the solver at the beginning of the puzzle.

Rules: Standard sudoku rules apply. 

Digits cannot repeat in cages and the sum of the digits in a cage must sum to the number in the corner of the cage (If you know CTC's secret, those clues are unnecessary). 

Digits in thermometers increase from the bulb.

The digits 1 through 9 appear exactly once on each long diagonal.

To start the puzzle, pick any two numbers from 1, 3, 5, 6, 7, 8, 9 and put them into the highlighted dominos in the same order (for example, if r3c4 is 9 and r4c4 is 8, then r5c9 and r6c6 should both be 9 and r6c9 and r7c6 should both be 8). Now you should have a puzzle with a unique solution. 

Thanks to Supraduko and SudokuWiki, whose software was immensely helpful in building this, and to Cracking the Cryptic for renewing my interest in sudoku and introducing me to killer/thermo rulesets among others.