Remedy to chant Om and Beej mantra without initiation. You just have to add a Nipaat.
For example, Om Namah Shivaay and Om Gam Ganapataye Namah, Om Kleem Krishnaay Namah, etc. You just have to add a Nipaat like Cha, Api, Iti, Tathaa, Eva etc. Like Om Namah Shivaaya Cha, Om Gam Ganapataye Nama Iti, Om Kleem Krishnaay NamasTatha. etc.
My guru told me and this is highly discussed and well known fact for deeksha mantra. Because Beej mantra are very harsh, but Nipaat takes the harsh overpowering energy and controls it, Nipaat even means "dropping". Because Nipaat are considered to be "dropped" , as in the sentence can still make sense if you remove or add them, Nipaat therefore allow you to get powers of Beej mantra and Pranava (Om) , without changing the meaning and takes the Beejakshar mantra's energy and drops it.
The reason why this has to be done is because, mantra have a structure. Om Namah Shivaaya, has to be chanted exactly like "Om Namah Shivaaya" , but because Om and Beejakshar require guru and initiation, so their energy becomes unstable or too much to control. But Nipaat drops that energy overflow along with itself. So "Om Namah Shivaaya Cha", still allows to chant the full mantra required according to structure (Om Namah Shivaaya structure), but Nipaat is dropped technically so it allows use of same mantra and structure without changing anything.
This is known in the vidya of mantras. Because words like Vicche, Vaushat, Vashat, Phat, Visphrem, Sphrem, Hum, Hum Phat, and sometimes Shraushat (Shraushat can be used for Devatas but is mostly used for Pitrs), these words don't have a meaning by themselves, but how mantras are structured required you to know where these parts of mantra is to be used and where to apply. For example, Svaha and Namah are also similar mantra-parts, Namah is most used and Svaha is also used. But with Svaha mantra it requires to give ahuti to Yajna, because it is Svaha. Namah technically doesn't have a meaning, but it's surface level meaning means "Praying".
Some Nipaat that are regular are Cha, Iti, Tatha, Api, Eva, Hi, Tatah. These are enough. And always add them in end. Honestly, you would also have to take care of Sandhi too, For example "Om Namah Shivaaya" -> "Om Namah Shivaaya Cha", but "Om Kleem Krishnaay Namah" -> "Om Kleem Krishnaay NamashCha". It is actually very easy, Sandhi is not that hard. But usually these 2 are the only variation with Cha, so Cha is pretty safe.
Earlier all various concepts like Chhand, sandhi, shabda, pada, nipaat, were known as natural understanding, but recently people know these grammar rules very less and fear that it is hard to learn, whereas it is so easy and inherent understanding. As you know mantra has Rishi, Chhand and Devata, because afterall mantra are spoken in words so it is important to know about Chhand and basic grammar and sandhi rules. Nipaat is one of most important and widely used words, throughout mantra tantra and scriptures, and were made to enhance the meaning of words without affecting the sentence. So chanting Beej mantra with Nipaat is very important. Chanting without Beej mantra or Om (Pranav) such as Namah Shivaay, it has limited benefits, this is why it takes so much time or feels hollow. It works, but it removes the very structure of Beejakshar and Om, but because we need something to drop the ugra energy, so the only option becomes using Nipaat words.