I don't believe that it is possible to transfer eligibility until and unless you actually have a dependent spouse or child. The VA website for transferability of benefits required the name and SSN of at least one dependent family member registered in DEERS. You need to get a (making a presumption) wife and then register for transferability of benefits. At that time you will incur the additional service obligation on which the transferability is conditioned. I don't believe that it is possible to register for transferability and the additional service obligation before you have a dependent. It would be nice if you could serve the four years before you actually met and married your wife but I don't believe it is an option.
Once you have a spouse or child registered for GI Bill benefits they must be used within 10 years of your leaving active duty IIRC. That may be a stretch for a newborn unless you are able to remain on active duty until the child it 8-12 years of age. If you are making it a career then there may be no rush at all.