Ah Ha, The plot thickens
Well my man, you are in luck.
First of all, DO NOT put anything on the earase heads. That would require some form of tape or something. That is bound to be a desaster.
With the deck you have, you can accomplish this with no problems.
Since you have 4 tracks to work with, you can record 3 tracks, then bounce those three tracks to the forth track. once those tracks are bounced, you have another 3 tracks to work with.
The only down side to this is that first of all, you will need to set your levels carefully when bouncing down to the forth track because once you start recording on tracks 1 - 3 again, the original recorded material will be erased. Secondly, in this situation, you will be dealing with a mono track. Because the info thats bounced down to track 4 is all on one track, you will not be able to pan the sound.
I hope this helps to clear things up for ya.
Peace
Joe