You don't need it. No Ryzen CPU will draw that much power unless overclocking on LN2. You could probably get along just fine using only one 4 pin connector.
But if you really wanted to put something there you have two choices: one is get another CPU/EPS cable from Thermaltake to put in an open connection point on your modular PSU. If you don't have an open connection point on the PSU, get a splitter to turn one of the existing 4-pins into two 4-pins.
Don't use a splitter if you really do plan on overclocking to 5+ Ghz on LN2. For that matter, don't use a 650W Thermaltake PSU either. But you'll not over-current the cable with any stock Ryzen CPU.