I would not use m4 as a donner cr2 . you would have to do to much work to clean up the cr2 to use it as a donner . A doner cr2 is seen in many dif ways some ppl think its  a bad thing to use one some do not As far as i KNow  you can use other clothing as a donner I use my own clothing as donner cr2's lmao  but then again I have a ton of clothing.
Ways to rigg I kow 3 ways to rigg clothing .

1. lets say you have a shirt wee a shirt and  its all modeled and clean you will want to group that shirt.
2. wee we have  a clean shirt thats all grouped
3. load m4 in poser
4. in port your shirt obj into poser
5. go right to the set up room
6. loaad m4 bones to the shirt
7. go back to the pose room confor the shirt
8. dance around and be happy coz you  just riged the shirt to m4
9. now go clean the shirts cr2 take dead prams and bones.

Ok to much lets work with a rigging tool I like Tool Collection for Poser By Dimension3D then again I like most all his stuff works well and he's a cool dude
I use his tool to  do what is called a base rigg . I run the tool it rigges my shirt wee i just need to add morphs thats a full other page .

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