It can be very challenging when no obvious career paths exist and any promotion is a minimum of a step-and-a-half away. I know because twice I dealt with it directly – once, at a company where I supervised a clerical support operation, and, again, at another where I managed a large Operator Services (switchboard) area. In both cases this was precisely the problem (and in neither case, was HR able to offer any advice or assistance).
So I took matters into my own hands by promoting individuals, anyway, into roles in other areas of my departments that had more established career paths. I knew they were under-qualified for these positions, but under the category of walking-my-talk about the respect/regard I said I had for the people I worked with, I felt these leaps-of-faith were risks worth taking.
Admittedly, it did not always work out very well. Sometimes the step-and-a-half jump proved just too much. But other times, they were able to rise to the challenge with only a little extra training and support. And the morale boost was unmistakable – both in the new areas, where the incumbents enjoyed the opportunities to nurture the newbies and show what THEY could do, and in the clerical and switchboard areas, where those still there now saw a bona fide path out if they worked hard enough and readied themselves properly. Even people not directly involved upped their game and started working harder, as a show of support for what we were doing. It became a source of "departmental pride" – and envy for those in other departments! Even when it didn't work out, to a person, they appreciated the opportunity they were given and thanked me on their way out the door.
I'm not saying that this is what you SHOULD do. I'm just sharing what I did. I can tell you, though, decades later, I still feel proud about how my leaps-of-faith changed people's lives for the better.