I'm a firm believer in avoiding super race-specific intervals at this point in training. You can hit race paces, but in a context that is very different from a race.
For example, a very race specific mile workout (to be avoided at this point) would be 4x600 @ mile pace w/ 1-2 min rest (depending on the desired intensity). This workout will build lactate in a similar manner to a mile race while allowing the runner to accumulate more than 1 mile at race pace.
At the point in the season, I would hit mile pace, but without accumulating those high levels of lactate. Some examples:
Alternations of 200/600 with the 200 @ mile pace/600 steady (slower than LT pace, about 90 sec/mile slower than mile race pace)
200s at mile pace w/ 200 meter jog (easy)
Ins and outs (1600 effort or a bit harder on the straights, jog the turns)
I agree with the poster who said to do "transitional" vo2 max work.
8 x 400 at 3k-5k pace w/ 3 min rest
4 x 800 at 5k pace w/ 5 min rest
Steady run w/ 3 min pickups at 5k pace
Mix in some aerobic work, like standard tempo runs, min on/min off fartleks, 5 min cruise intervals w/ 1-2 min rest
I would also have an aspiring miler work on all-out speed at this point (assuming they've done some transitional work at 800-mile pace)
4-6 x 10 sec hill sprints
4-6 x flying 50s
Building base by slogging endless easy miles is a myth. It works for some runners, but most can safely get a lot more out of winter/summer. Just don't make it too intense since you want them running their best in May and June.