Griffiths will provide cover at nine with Wales Under-20 international Tomos Williams set for a spell on the sidelines.
Williams suffered an ankle injury in the pre-season victory over Bristol Rugby and is to miss several months of action as he starts his rehabilitation.
Wales Sevens contracted player Griffiths, 30, will link-up with Cardiff Blues following an agreement between the region and the WRU.
The Bridgend-born back, a former Under-19 and Under-21 international, started his career with Bridgend Ravens before spells with the Ospreys, Cornish Pirates, Doncaster and Newport Gwent Dragons.
Griffiths joined Jersey in 2010 and scored 13 tries in 58 games for the island side and was instrumental in helping them win promotion from National One to the Championship in England.
Griffiths made his debut on the Sevens circuit in Adelaide in 2011 and returned to the World Series for round four of the 2014/15 series in Wellington.
Attack Coach Paul John said: “I’ve worked with Nicky before on the Sevens circuit and he is a talented player who will be keen to make a positive impression during his time with us.
“It’s a great shame that Tomos suffered the injury against Bristol, particularly after such an impressive pre-season, and with Lloyd Williams away on Wales duty ahead of the Rugby World Cup it was vital we added strength in this position.
“Our thanks go to the Wales Sevens set-up for helping us reach this agreement. With no tournament until the end of the year, the deal is beneficial to all parties and we look forward to Nicky joining up with us.”
Steff Thomas, Wales Sevens Team Manager, said: “Following an approach from the Cardiff Blues, we are happy for Nicky to act as scrum half cover after the unfortunate injury to Tomos Williams.
“This is an excellent opportunity for Nicky. His move to Cardiff Blues also fosters the link between Wales Sevens and the regions and enhances the good relationship we have with the regions in readiness for our new season ahead with begins in Dubai in December.”
