No, those constructions are ungrammatical.
When the verb is in the present, the temporal reference for still is the present moment following upon a stretch of time immediately preceding:
He is still working here now | today after three years on the job.
or a past reference point when the verb is in the past:
He was still working here then | at that time after three years on the job.
for the last three years refers to a stretch of time extending from a point in time three years ago up until the present moment, and thus it partners well with the present perfect:
He has been working here [now] for the last three years.
We can also shift the present moment to a reference moment in the past, and use the past perfect:
He had been working there [then] for the last three years.