"トムはずっと勉強をしている。"
If "since when Tom has been studying" is not hinted in the context, this sentence could be interpreted as "Tom is studying continuously without break" or "Tom is eternally studying".

Japanese is a very context dependent language and unless I venture to used words probably never used by the most people, stating the above in present perfect continuous aspect is not possible; particularly because of the lack of "since when" in the original sentence.

Present perfect continuous aspect exists in Japanese. But unlike in English, particles and certain words seem to take care of them; and somehow I can't think of any generic rule for making a perfect continuous sentence in Japanese.

Some examples:
Tom has been studying bears for three years.
トムは三年に渡ってクマの研究をしてきた。
トムは三年に渡ってクマの研究をしている。
The key word is"三年に渡って" for the duration of three years.
By the way, semantically, these two are identical and even when their aspects are considered, they are the same.
They are different, however.
The former gives an impression of landing at the present and tends to divert the readers' attention to Tom's present, how things has changed etc, and provides no hint as to the future; as "きた" has a sense approximately equals arrived or has come.
The later has a stronger emphasis on continuity and the ongoing nature of his study and hints that his study will not be interrupted any time soon.

私達は生まれてからずっと一緒なんです。
We have been together ever since our birth.
"生まれてからずっと" is the key word; "ずっと"is used to stress continuity, therefore, continuously ever since birth.

空を見続けている。
Having been looking at the sky.
The subject of the sentence is omitted; it may have been given in the earlier sentence or is to be presented later.
The key word is "続けている"; describes the action to be continuous. And as the sentence is in present continuous tense, if the action is continuous, then it must have started at some point in the past and continued to the present.

I'm quite sure, there are lot more of these but I can't think any more of them at the moment.