Look in the 920 definition file and find the line that I bolded below and add what's in the code blocks directly under it. Play around with the padding in blue to suit your own needs.
<convinput id=atom(convinput) cmdid=700 xscrollable=false margin=Rect(4,0,0,0) padding=Rect(0,1,0,1)/>
code:
<element layoutpos=right layout=BorderLayout() borderthickness=Rect(0,0,0,0) bordercolor=rcclr("msgr",20755) padding=Rect(5,2,5,2)>
<element id=atom(paddedsendbutton) layout=FillLayout() padding=Rect(25,25,0,0)>
<element class="SendButtonBk" layout=FillLayout() id=atom(sendbtnbk)>
<Button id=atom(sendbtn) cmdid=272 ShortcutString=rcstr("msgr",60014) AccDesc=rcstr("msgr",77) Content=rcstr("msgr",60014) Class="PushButton" AccName=rcstr("msgr",60058) AccDefAction=rcstr("msgr",20500) MinSize=Size(72rp,rcint(20501)) Padding=rcrect(20530) Margin=Rect(0,0,0,0) DialogStyle=0x01|0x02/>
</element>
</element>
</element>
