Good idea and I have tried this theory recently and indeed it does work, but it only works for Armoury Items (which are):
€–C 80 96 43 Fire Crackers
€—C 80 97 43 Slingshot
.˜C 00 98 43 Slingshot (Stone)
€˜C 80 98 43 Spudgun
.™C 00 99 43 Super Slingshot
€™C 80 99 43 Bottle Rockets
.šC 00 9A 43 Pack of Bottle Rockets
€šC 80 9A 43 Stink Bombs
.œC 00 9C 43 Carton of Eggs
.žC 00 9E 43 Can of Spuds
. C 00 A0 43 Newspapers
€ C 80 A0 43 Spray Paint
.¡C 00 A1 43 Super Slingshot (Stone)
€¢C 80 A2 43 Rubber Band Ball
.¤C 00 A4 43 Camera
€®C 80 AE 43 Bag Of Marbles
.ÅC 00 C5 43 Itching Powder
.ÆC 00 C6 43 Super Spudgun
.ÕC 00 D5 43 Digital Camera
€ÚC 80 DA 43 Skateboard
I did try this with the trophy and other items and all that came up was a white square (like it does with the pedstats method on certain items), which does clarify that the items are scripted to appear a certain way:
Hi, Algies Jacket is from a side a mission, it MAY appear in the key items, the possition of the items in the shop determines if a item is taken into the key items or weapons slot, eg if i replaced the floweres with the newspapers i wouldn't get the papers as a weapon just a key item only, some of these key items don't appear also, you will either get them as a white square or just won't see them at all, me and mad will be releasing this method v soon if not within the next few days
I also tried this with that blasted joke candy and the same thing came up, which is somewhat odd as if you look at the model list it should crash when spawned as pedstats or as a direct model, which does lead me to believe that this hidden weapon was meant to appear scripted in a cutscene of somesort hense why it still has its animation groups attached to it "W_PRANK.W_Thrown"