Why wait 4 years? Why not join a startup (or technical company) now and start doing the things you want full-time instead of fitting them in around a job you don't value? You can learn
a lot getting hands-on at the ground level, and if you want a mix of tech skills
and business savvy then why not work at several startups (over time) and help grow them - you may get to do everything and anything from software/service design to marketing and PR. It is probably the best experience you can get if your aim is to start your own startup and will also equip you well for applying to places like Google.
If you really have to stay at the job for some reason, then I'd say in your spare time practice programming and building web apps around what you are interested and that solve problems you face. Launch them and see what happens. You may suck/fail at first, but over time you will definitely learn a lot, and will get better with each iteration you take - you never know one of them may really take off. You can practice business skills in growing your apps and once you have done it a few times, try doing it for other businesses (ideally in other fields too for some diversity to other markets). There are many courses/books that can teach you the skills, but if possible, find someone whose expertise you respect to mentor you.
Many successful businesses were, and still are, started by people in the same boat so please don't let worries about lack of skill/experience stop you from starting.