If you think impartially, no one has seen any of these gods Shiva, Ganesh, Mangal, Lakshmi, Hanuman, Shani, etc., nor has anyone heard any of them speak. It is Man who has created these and very many other gods, out of his own (man's own) imagination, and, again, it is Man who has laid down rules about when, how and why to do puja to all these gods. What has happened is all these man-made ideas, rules and regulations have been effectively instilled into people's brains with so much efficiency that people get worked up when this simple fact is told, and people get worried if they are, for some reason, unable to follow any of these ideas (with which they have been deeply brainwashed). (You will find many posts rebutting this view; all those are only proofs, if proofs are required, for the truth in what I have written above.)
Therefore, there is no need to worry about aspects/difficulties such as the one you have raised in your Original Post. These gods are your own mental creations and the puja you are doing is also as per your mental plans. Anything goes!
But, if you have to follow the written down rules in the scriptures regarding puja, one has to do a complete puja, and no shortcuts are allowed; the Bhagavadgita verse cited in one of the above posts only says that "'If one offers Me with love and devotion a leaf, a flower, a fruit or water, I will accept it.'"; it does not say (rather Krishna did not say) that this alone would be sufficient as puja; that is clever twist given by our priesthood in extolling the Geetha. What it means that anything offered without "Bhakti" (and bhakti does not mean 'love and devotion'; its meaning is different and cannot be expressed in English) will not be accepted by Krishna; it will be summarily rejected.
My forefathers used to say that any puja half done is a very serious sin and will haunt you for the next 2 x 7 = 14 rebirths as one of the mahaapaatakams.
So, finally, it is up to you to decide which route to take!
