Yes it is possible, I made a posting about this on 04/30/09, under the heading of steering head bearing lubrication, I used a length of threaded rod, two large area rubber grommets, two large area steel washers and two nuts .
I put a rubber grommet and large area washer and a nut on one end, inserted the rod through the bottom end of the steering tube, it comes out on top at the 10mm hex in the adjustment nut for the steering bearings .
I put the other rubber grommet, large area washer and nut on the threaded rod, tightened the nuts to get a good seal .
I screwed in a 90 degree grease fitting in one of the threaded holes, and plugged the other hole, and pumped grease into the cavity until grease came out around the bearing areas .
Only concern I would have about doing this, is that in cold weather, the grease may stiffen up, and cause 'heavy' steering .
I use Aeroshell 33 grease, it doesn't change 'viscosity', (probably not a correct term for grease), it doesn't get thicker, or stiffen up at temperatures as low as -10 F.
As long as you know your bearings are in good condition, this may be an option available to you .
If you have never have had a look at the bearings, I think it would be wise to do it once, before doing this procedure .
