Google images for indoor vegtable gardening copy and print some pics then brag about them to the grow shop as your own grow project.
Being into horticulture, especially indoor growing of tomatoes, flowers etc. is, I think, a good idea in general. You might find some info that you can use in some obscure flower growing forum, having the background knowledge, the background trail, and even some actual 'legal' things growing will, imo, go a long ways in having a great cover story. Not that any cops would get a wiff of what your doing, take your vehicle plate # down in the garden store parking lot and question the staff about what you buy and what they think you are using trhe supplies for...but if something like that were ever to happen rest assured everyone would you are in contact with would know you as a well-informed legitimate horticulturalist. Not that the utility guy (gas company, telephone and or cable guy, or any EMT other official that you or a loved one had summoned to your home) would be in any area doing their work (like your cellar, or attic, or the bedroom you having cable tv installed in) and happen to notice all of the indoor horticultural stuff, or god forbid your grow tent....but if they just happened to and along with the grow-tent and horticultural stuff they saw a bunch of books about flowers, maybe some fresh flowers etc.....that would be an ice cold trail. Personally, I would rather have an ice-cold trail than even a luke-warm one. As a matter of fact, I grow flowers and tomatoes only, indoors, and find the vast horticultural knowledge, and practical indoor solutions applied by marijuana growers to be top-notch, and often far more cost-effective than the solutions and practical general indoor horticulural advice discussed and suggested on the forums of most "legitimate" horticulatural growers.
i think going to the big bargain stores is the way to go. those people don't own the business, and no one will ever remember you unless you walk up to them stoned as fuck and are like "uhhh yea, i uhhh need some 5 gallon buckets, florescent lights, and soil."
ya know another reason people would buy that much starter mix, perilite, soil is to make decorative outdoor container floral arrangements. You'd easily go through a couple bags of soil, some peat, perlite, worm castings, a little cow manure.