It isn't easy. When it does happen, it's more like a NG officer that finishes grad / medical / law school and go on to active duty as a JAG, RN, Dentist, MD or something like that. There was also, back in the day, a program where the top students at their basic course got an offer of active duty if they were RC soldeirs.
That being said... Every reserve component unit has several soldiers and officers that are full time reservists. The Army Reserve and NG has a program where they can put you on full time orders for four years at a time to administratively support the reserve unit. (After all, the unit can't run with people only showing up one weekend per month!) There is plenty of work to do M-F, and those Active Gaurd / Reserve (AGR) soldiers keep the machine running througout the month. Most AGR soldiers and officers string five or more of those tours together and retire as 'full timers" with regular retirement benefits. And, if they plan it right, they can stay generally in the same area for all twenty years of their military career and not have to drag a family all over the globe.