Give each skill (hidden under the covers) two skill levels - the STUDY level
and the USE level. Each would be advanced as under the current scheme, with
decaying returns as you seek higher and higher levels. They would however grow
slower than currently, and have a lower cap - say that study has a mximum level
of 7, but 7 is as hard to achieve as 10 is currently. The USE level maximum
would be 3, but would take a long time. Now, the level you work at, and the
level you see in your report, is the sum of the two levels.
What this means is that someone can do pure STUDY on a skill, but could
only reach level 7 maximum without USEing the skill, and it would take a while.
A player could also just USE the skill, and again he could only reach level
3, with this takening a very long time. However, a player would find for
swiftest advancement he would spend 7 days studying for every 3 days working.
The numbers need juggling, but the idea is important. Make both STUDY and
USE important for advancement, with neither one in isolation getting you to
the maximum level.