The Warriors take on Edinburgh at Murrayfield on Boxing Day (ko 7.30pm) and at Firhill a week later (Jan 2, ko 3.00pm).
Johnnie told the Daily Record: "People always talk of these Christmas and New Year matches as being unofficial Scotland trials and that's exactly how I intend to treat them.
"The past few months have not gone to plan for me as regards involvement in the national squad so I know I have quite a bit of work to do if I am to be in the Six Nations picture.
"It was a massive disappointment when I wasn't even included in the Scotland training group that went to Spain before the autumn internationals.
"But I have had setbacks like that before and they just make you all the more focused and determined to get back.
"The Glasgow coaches, Sean Lineen, Shade Munro and Gary Mercer, have been very supportive, telling me what I need to do to have a chance of a recall. The games against Edinburgh will be my opportunity to put down a marker."