Using sea buckthorn syrup in brewing

[HugoJM]

Hi all. Looking to brew a sea buckthorn gose. Can't find any dried or fresh sea buckthorn locally, but can find a sea buckthorn syrup. Only ingredients are sea buckthorn, cane sugar and water. How much should I add and when for a 5.5 gal (21 L) batch? I was thinking around 6 oz at the end of boil/whirlpool. Some people are saying at bottling, but I'm worried about gushers with the cane sugar. Thanks!