Hi, good question... not something I've done so hopefully you get some "voice of experience" answers soon...
The method I've seen described before is insulated blocks - minimum 2 per train - and relays that trip when the loco's lead wheels close the insulated gap. I think it's the outer rails that are insulated, but it might be the center rail.
Is this a single-oval line? That's about 30 feet of track. If you set up 6 even blocks, to keep one unpowered block between each train's powered block, you've got 5 feet per block. I think your trains must all be short enough to clear the block behind them before the next train hits it, so you might be limited to trains of 3-4 feet in length - depending on speed differences of your locos at the track voltage you run.