ponczo_: Unfortunately, we cannot move games between GOG accounts or merge them :(
However, if you use GOG GALAXY, you can access all your games in a convenient way without changing accounts. To do that, simply download and install the game from your second account, log into your main GOG account in GOG GALAXY and click on the settings icon (upper left corner) > Add games & friend > Add game manually. After that, you will be able to launch the game via GOG GALAXY using your main account. Your save files will be stored locally, but the application will count your playtime.
Please also remember that our games are DRM-free and it's not necessary to use GOG GALAXY at all - you can launch every GOG game by using .exe file in game's installation folder. If you install games directly to the GOG Galaxy games folder (for example using the offline installer), they are also added to Galaxy automatically, at least for me.