Davies underwent shoulder surgery after Wales' win over Argentina a week-and-a-half ago and faces a significant spell on the sidelines as a result, while Reed is currently out with a toe problem.
Blues boss Phil Davies spoke earlier this week about his desire to bring in new faces to fill the void and Dicomidis has finally been handed a chance to impress at regional level after regularly shining in Welsh Rugby's second tier.
"We're really pleased that Chris will join the region. He is a fine player who has played extremely well for Pontypridd over the last decade," said Davies.
"Chris is someone I know very well and also Chief (defence coach Dale McIntosh) has a very close relationship with him from their time together at Ponty.
"He will strengthen our second row resources, with Lou Reed and Bradley Davies currently sidelined, and I know he is determined to take this opportunity. We are excited to see what he can achieve in a full-time professional environment."
Dicomidis was club captain at Pontypridd in 2010 and has been a first-team regular for much of the past decade despite still being just 28 years of age.
The 6ft 6in, 18st 6lbs lock is relishing the chance to show he can cut it at the top level and could even feature when the Blues return to Heineken Cup action in December's double header with Glasgow Warriors.
"I'm excited about the opportunity to become part of the Blues squad and taking my chance at professional rugby," said Dicomidis, who has represented Wales at U19, U21 and University level and has also played for the Barbarians, as well as Cyprus.
"You always hope you'll get the call to join a full-time set-up and I've spoken to Dale about the region and what is expected. I'm determined to grasp this opportunity with both hands and show what I can achieve.
"I join up with Blues next week and can't wait to get started in a new environment and really push myself to show what I am capable of."
The Blues could yet announce another new signing before they face Glasgow in the Welsh capital a week on Friday as Davies is keen to bring in some backline cover following injuries to centre Cory Allen, fly-half Rhys Patchell and wing Harry Robinson.