Yes, of course it is possible. How do you think people learned English before SuperMemo existed? :)
I think I understand what you mean by "too busy to spend time in front of a computer". When you are reading an interesting article or listening to an interesting podcast, you are not only learning English -- you are doing something fun at the same time. So, in a way, you are not really "spending time on English".
With SuperMemo, you are just learning English; there are no other benefits -- unless you are one of those who simply like making and reviewing items in SuperMemo. I am one of those people. Expanding a SuperMemo collection gives me the feeling of "growing something" (my collection and my own "language power"). When I review items, I feel less good, but I also enjoy it to some degree -- partially because it is challenging.
I am in fact thinking about a new article about how to use SuperMemo and what it is good for. I'll share just a few thoughts right now:
1.You can learn through input alone.
2.SM lets you make steady progress without massive input. For example, if you are a beginner and cannot get massive input because you suck at comprehension. Or, you don't have time for lots of input, but want to make some progress anyway.
3.For someone who has enough comprehension and enough interests to get a lot of fun input in English, the usefulness of SM is limited. Here are the main uses:
•eliminating your mistakes by adding corrected sentences to SM (which ensures their repetition)
•adding useful things that you just keep forgetting (e.g. words that just don't stick in your memory)
•adding useful phrases that don't occur in your input, or occur rarely (e.g. handy spoken expressions that you won't find in podcasts, books, websites, or whatever input you get)
•adding pronunciations for words that don't occur in your spoken input frequently enough
4.Adding words/phrases/structures that occur in your input frequently (say, more than once in 1-2 months) is a waste of time because you are reviewing them anyway as you get input. You don't need artificial reviews for these.
In short, I believe SuperMemo is always useful, but it is less useful for people who can get massive input. However, if you use SM according to the four bullet points above, it shouldn't take too much of your time because you will only be adding selected information instead of adding every sentence from every text you read.